VIVIAN'S  EVERYDAY  CHEMISTRY 
MOORE  AND  HALLIGAN'S  PLANT  PRODUCTION 
TORMEY  AND  LAWRY'S  ANIMAL  HUSBANDRY 

EDITED  BY 
KIRK  LESTER  HATCH,   B.S. 

PROFESSOR   OF  AGRICULTURAL   EDUCATION 
UNIVERSITY   OF  WISCONSIN,   MADISON 


EVERYDAY    CHEMISTRY 


BY 

ALFRED   VIVIAN 

DEAN  OF  THE  COLLEGE  OF  AGRICULTURE  OF 
THE  OHIO  STATE  UNIVERSITY 


AMERICAN   BOOK   COMPANY 

NEW  YORK  CINCINNATI  CHICAGO 

BOSTON  ATLANTA 


COPYRIGHT,  1920,  BY 
AMERICAN  BOOK   COMPANY 

All  rights  reserved 

VIYIAN'8  EVERYDAY   CHEMISTRY 
W.   P.      3 

EDUCATION  LIBR* 


" 


UAxV—  • 


GENERAL   INTRODUCTION 

THIS  series  of  texts  is  based  on  the  theory  that  the  success- 
ful citizen  should  know  the  chemical,  physical,  and  biological 
forces  with  which  he  has  to  contend  ;  that  he  should  under- 
stand the  laws  under  which  these  forces  operate;  and  that 
he  should  acquire  some  skill  in  directing  them.  He  should 
ultimately  become  able  to  adjust  and  correlate  these  forces 
so  as  to  bring  them  all  under  the  orderly  operation  of  economic 
law.  In  conformity  with  the  above  theory  this  series  has 
been  made  to  cover  the  following  fundamental  divisions  : 

1.  The  science  and  art  of  chemistry  as  applied  to  everyday  Ufa, 
with  special  emphasis  on  household  economics,  soil  fertility,  and 
the  relation  of  chemistry  to  plant  and  animal  production. 

2.  The  science  and  art  of  producing  plants. 

3.  The  production,  care,  and  management  of  farm  animals. 

4.  The  proper  balance  and  combination   of  these  aspects  of 
household  economics  and  agricultural  production,  in  the  business 
management  of  the  farm. 

KIRK  LESTER  HATCH. 


M577057 


PREFACE 

THE  ordinary  high-school  course  in  chemistry  in  the  past 
has  consisted  of  a  condensed  treatment  of  the  subject  of  in- 
organic chemistry,  which  was  intended  to  prepare  for  the 
further  study  of  that  subject  in  college.  The  principal  ob- 
jection to  a  high-school  course  consisting  entirely  of  inor- 
ganic chemistry  lies  in  the  fact  that  the  ninety  per  cent  of  the 
pupils,  who  do  not  go  to  college  and  who  pursue  the  subject 
no  farther,  are  left  with  a  very  faint  conception  of  the  in- 
timate relation  which  chemical  phenomena  bear  to  daily 
life.  Such  pupils  are  therefore  likely  to  think  of  chemical 
changes  as  occurring  only  in  beakers  and  in  test  tubes. 

The  reaction  against  the  old  type  of  high-school  course 
in  chemistry  has  resulted  in  the  publication  of  a  new  type  of 
textbooks  for  secondary  schools.  In  these  the  authors 
have  gone  to  the  other  extreme  by  attempting  to  present 
the  applications  of  chemistry  to  daily  life  without  any  ground- 
work in  the  fundamental  chemistry  of  the  elements,  a 
knowledge  of  which  is  necessary  to  the  understanding  of 
chemical  compositions  and  reactions. 

This  text  follows  a  middle  course,  and  while  the  outstand- 
ing feature  is  its  treatment  of  the  applications  of  chemistry, 
inorganic  and  organic,  the  presentation  is  based  on  a  brief 
study  of  the  elements  and  their  important  compounds  and 
reactions.  The  preparation  of  such  a  book  is  made  difficult 
by  the  enormous  mass  of  facts  and  theories  from  which 
must  be  selected  those  which  are  vital  to  the  purpose  of  the 
text.  Two  questions  have  been  asked  regarding  each  fa'ct 
and  theory  —  (1)  is  this  fact  or  theory  essential  to  the 
understanding  of  any  of  the  phenomena  of  daily  life,  or 
(2)  is  it  necessary  to  explain  some  other  fact  or  theory 
that  is  essential  to  such  an  understanding?  Unless  the 
answer  to  one  of  these  questions  is  affirmative  the  subject 

7 


8  PREFACE 

in  question  is  excluded  from  the  text.  The  only  excep- 
tions to  this  rule  are  a  few  subjects  proved  by  experience 
to  be  of  especial  value  in  holding  the  interest  of  the  pupil. 
Much  of  the  theory  included  in  the  older  texts  is  excluded 
because  of  the  feeling  that  a  first  course  in  chemistry 
should  deal  largely  with  facts  and  that  the  theoretical  con- 
siderations should  be  left  to  a  more  advanced  course.  The 
chemistry  of  the  elements  has  been  confined  to  a  score  of 
elements  that  are  of  common  occurrence.  The  study  begins 
with  the  element  itself  if  it  is  commonly  known,  but  with 
a  compound  in  case  the  element  is  not  a  familiar  substance. 
In  other  words,  the  procedure  is  always  from  the  known  to 
the  related  unknown. 

The  small  high  school  which  cannot  afford  expensive 
equipment  has  been  constantly  in  mind  during  the  prepara- 
tion of  this  text.  The  exercises  call  for  no  complicated 
apparatus ;  most  of  the  experiments  may  be  performed  by 
means  of  simple  homemade  devices,  or  even  in  many  cases 
by  the  use  of  kitchen  utensils. 

No  one  group  of  pupils  should  be  required  to  use  all  the 
material  in  this  book,  since  a  wide  range  of  topics  has  been 
treated  in  order  to  meet  the  varying  needs  of  boys  and  girls. 
After  the  first  thirty-five  chapters  have  been  completed  the 
boys  and  girls  may  be  separated  and  allowed  to  study  those 
chapters  which  are  of  particular  interest  to  each  group. 
This  book  is  especially  suitable  for  use  in  the  vocational 
courses  in  agriculture  and  home  economics  which  are  being 
introduced  in  many  high  schools. 

Photographs  for  illustrations  have  been  furnished  by: 
Ohio  Experiment  Station,  Frontispiece  and  Figs.  174,  225, 
229,  231,  242,  244;  Montana  Experiment  Station,  Figs. 
210,  211;  Illinois  Experiment  Station,  Fig.  236 ;  L.  H. 
Guldard,  Figs.  92,  237;  Jeffrey  Manufacturing  Company, 
Figs.  227,  228 ;  Dr.  E.  V.  McCullum,  Fig.  159. 


A  WORD   TO   THE   TEACHER 

THE  success  of  a  course  in  chemistry  depends  largely  upon 
the  character  of  the  laboratory  work.  Without  the  performance 
of  laboratory  exercises  the  study  of  chemistry  degenerates  into 
a  mere  act  of  memorizing.  On  the  other  hand,  nothing  is 
more  pernicious  than  unsupervised  laboratory  work,  since  it 
not  only  wastes  the  time  of  the  pupil  but  creates  bad  mental 
habits.  The  earnest  teacher  of  chemistry  will  keep  in  close 
touch  with  the  pupils  throughout  the  course. 

In  small  high  schools  where  the  class  in  chemistry  does  not 
include  more  than  ten  to  fifteen  pupils,  it  is  a  mistake  to  divide 
the  time  allotted  to  chemistry  into  recitation  and  laboratory 
periods.  The  teacher  should  be  at  liberty  to  use  each  period  or 
part  of  a  period  for  recitation  or  experimental  work  as  the 
progress  of  the  subject  suggests ;  or  better  still,  the  experiment 
and  the  recitation  should  be  coincident. 

While  it  is  desirable  to  have  all  the  pupils  perform  each 
experiment,  such  a  procedure  is  not  absolutely  essential  to  an 
understanding  of  the  subject.  Where  the  equipment  is  meager, 
very  good  results  may  be  obtained  by  having  the  class  gather 
around  the  laboratory  table  and  having  each  student  in  turn 
perform  an  experiment  while  all  members  of  the  class  take  notes. 
This  method  gives  the  teacher  an  opportunity  to  have  the 
class  recite  under  the  most  favorable  circumstances  and  espe- 
cially to  test  the  pupils'  powers  of  inductive  reasoning.  It  also 
tends  to  develop  that  kind  of  comradeship  between  pupil  and 
teacher  which  is  the  successful  teacher's  greatest  asset. 

The  teacher  in  the  small  high  school  needs  no  longer  to  hesitate 
to  introduce  chemistry  because  of  the  cost  of  apparatus.  Most 
of  the  experiments  in  this  text  may  be  conducted  with  equip- 
ment which  is  at  hand.  By  the  exercise  of  a  little  ingenuity 
the  remaining  apparatus  can  be  prepared  from  comparatively 
inexpensive  materials.  Common  glass  tumblers  may  be  used 
in  place  of  beakers  when  the  application  of  heat  is  not  neces- 
sary. Granite  ware  or  porcelain-lined  kitchen  cups  may  be 
used  in  heating  all  liquids  except  very  concentrated  alkalies 
and  acids.  The  only  advantage  in  the  use  of  glass  beakers  is 
that  the  experiment  may  be  more  readily  observed.  Much  of 

9 


10  A  WORD  TO  THE   TEACHER 

the  needed  material  may  be  collected  locally  by  teacher  and 
pupils,  and  many  manufacturers  are  glad  to  furnish  samples  of 
their  products  gratuitously  for  use  in  the  classroom. 

It  is  not  possible  to  eliminate  from  the  course  in  chemistry 
the  teacher,  upon  whom  the  success  of  the  course  depends  more 
than  upon  any  textbook  or  laboratory  guide.  For  this  reason 
the  author  has  purposely  omitted  detailed  descriptions  of  the 
laboratory  experiments,  leaving  the  specific  directions  to  the 
teacher,  who  will  have  to  give  these  directions  in  any  event,  no 
matter  how  complete  the  descriptions  in  the  laboratory  guide 
appear  to  be.  The  larger  texts  on  chemistry,  to  which  the  teacher 
should  refer,  will  give  much  assistance  in  arranging  the  details 
of  the  experiment. 

The  questions  found  in  the  exercises  at  the  end  of  the 
chapters  are  merely  suggestive,  and  many, more  will  occur  to 
the  teacher.  Their  principal  value  is  in  enabling  the  pupils 
to  test  their  own  knowledge  of  the  subject.  The  teacher 
should  insist  that  the  pupils  look  up  every  cross  reference  that 
is  found  in  the  text.  Additional  reading  should  be  assigned 
on  many  of  the  topics,  and  it  will  be  well  to  have  each  pupil 
report  to  the  class  upon  certain  topics  which  have  been  assigned 
as  supplemental  work.  Most  high  schools  own  a  good  encyclo- 
pedia, and  at  least  one  article  in  the  encyclopedia  may  be  found 
which  is  germane  to  the  matter  discussed  in  each  chapter  of 
this  text.  The  agricultural  colleges  of  the  several  states,  as 
well  as  the  United  States  Department  of  Agriculture,  publish 
bulletins  for  free  distribution,  many  of  which  bear  upon  sub- 
jects discussed  in  this  book.  In  many  cases  these  bulletins  ap- 
peal as  much  to  the  interest  of  people  living  in  the  city  as  to 
those  in  the  country.  Such  pamphlets  should  be  procured  for 
the  school  library. 

The  high-school  curriculum  should  fit  the  community  in 
which  the  school  is  located,  and  the  chemistry  teacher  has  the 
opportunity  of  bringing  his  subject  into  close  relationship  with 
the  daily  life  of  the  pupils.  Chemical  processes  which  are  of 
unusual  interest  to  the  community  should  be  emphasized,  both 
in  the  classroom  and  by  means  of  excursions  to  points  where 
these  processes  may  be  observed.  Chemistry  should  be  made  to 
assist  the  pupil  in  interpreting  life.  Above  all,  the  teacher  of 
chemistry  should  remember  that  the  most  important  thing  to  be 
considered  is  the  pupil  and  not  the  subject  that  is  being  taught. 


FIG.  1. 


INTRODUCTORY   LABORATORY 
MANIPULATIONS 

CHEMISTRY  is  essentially  a  laboratory  study  and  is  readily 
understood  only  when  the  statements  of  the  text  are  illus- 
trated by  suitable  exercises.  As  certain 
laboratory  appliances  and  processes  will 
be  used  repeatedly  during  the  course,  the 
student  should  first  familiarize  himself 
with  them. 

The  Bunsen  burner  is  used  as  a  source 
of  heat  in  most  laboratories  where  gas  is 
available.  A  common  form  of  the  burner 
is  shown  in  Fig.  1.  It  is  attached  to  the 
gas  cock  by  a  piece  of  rubber  tubing.  When  the  gas  is 
turned  on,  the  current  of  gas  draws  air  through  the  holes 
at  the  bottom  of  the  tube,  and  this  mixture  when  lighted 
burns  with  an  almost  colorless  flame,  which  is  very  hot  and 
deposits  no  soot.  The  air  supply  may  be  reduced  or  entirely 
cut  off  by  turning  the  ring  at  the  bottom  of  the  burner  so 
that  the  hole's  in  the  tube  are  closed.  As  the  air  supply  is 
lessened,  the  flame  gradually  becomes  yel- 
low and  deposits  soot.  The  colorless 
flame  is  used  in  all  experiments  unless 
the  directions  state  otherwise. 

The  alcohol  lamp  is  ordinarily  used  in 
laboratories  where  a  supply  of  gas  is  not 
available.      The   simple    form    shown   in 
Fig.  2  is  the  most  common.     Such  a  lamp 
11 


FIG.  2. 


12     INTRODUCTORY  LABORATORY  MANIPULATIONS 


FIG.  3. 


may  be  made  in  the  laboratory  from  an  ink  bottle  or  an 
oil  can  and  a  little  candle  wicking.  When  a  more  in- 
tense heat  is  required  the  type  of  alcohol 
lamp  shown  in  Fig.  3  or  Fig.  4  may  be  used. 
In  such  a  lamp  the  alcohol  is  converted  into 
a  vapor  before  it  is  burned.  With  proper 
precautions,  the  blow  torch  used  by  plumbers 
and  painters  (Fig.  5),  in  which  gasoline  vapor 
is  burned,  may  be  used  when  high 
temperatures  are  needed;  but  gaso- 
line requires  more  careful  handling  than  does  alcohol. 
Glass  Working.  To  cut  a  piece  of  glass  tubing, 
make  a  deep  scratch  at  the  desired  point  with  a 
triangular  file.  Grasp  the  tubing  in  both  hands 
with  the  thumbs  back  of  the  scratch  (Fig. 
G)  and  pull  the  tubing  apart,  at  the  same 
time  exerting  a  slight  forward 
pressure  of  the  thumbs.  If  the 
tubing  does  not  break  easily, 
make  a  deeper  scratch  with  the 
file.  Never  use  much  pressure  in 
breaking  the  tubing. 

Smooth  the  ends  of  all  glass  tubing  or  glass  rods  by  hold- 
ing them  in  the  flame  of  the  burner  until  the  glass  fuses 
(Fig.  7).  If  desired,  the  end  of  the  tubing  may  be  closed 
entirely  by  holding  it  in  the  burner  until 
the  edges  fuse  together. 

To  bend  glass  tubing,  place  the  wing 
top  (Fig.  8)  on  the  burner  and  hold  the 
tubing  in  the  upper  part  of  the  flame 
until  the  loose  end  begins  to  drop  of  its 
own  weight.  Then  grasp  the  loose  end  FIG.  5. 


FIG.  4. 


INTRODUCTORY   LABORATORY  MANIPULATIONS      13 


and  bend  to  the  desired  angle.  Avoid 
bends  like  A  and  B  in  Fig.  9,  which  are 
due  to  heating  too  small  an  area  of  the 
tube. 

A  glass  tube  may  be  drawn  out  by  heat- 
ing a  small  area  in  the  point  of  the  flame 
(Fig.  10)  until  the  glass  is  quite  soft  and 

the  walls  of  the 
tube  are  thick- 
ened. The  tube 

must  be  rotated  in  the  flame  dur- 
ing heating.  Remove  the  tube 
from  the  flame  and  draw  it  gently  in  a  horizontal  position 
until  it  is  reduced  to  the  desired  size  (Fig.  11). 


FIG.  7. 


FIG.  6. 


FIG.  8. 


FIG.  9. 


FIG.  10. 


FIG.  11. 


14    INTRODUCTORY   LABORATORY  MANIPULATIONS 


FIG.  12. 


Wash  Bottle.  Make  a  wash  bottle 
similar  to  Fig.  12.  This  will  be  found 
useful  in  many  ways  in  the  laboratory. 
By  blowing  in  the  tube  (A)  a  small 
stream  of  water  is  forced  out  of  the  jet 
(B) .  A  piece  of  rubber  tubing  at  C  per- 
mits the  stream  to  be  guided  in  any 
direction. 

Holes  in  corks  are  usually  made  with 
a  cork  borer  (Fig.  13).  A  round  or  rat- 
tail  file  may  be  used,  the  hole  being  filed  out  until  it  is 
the  right  size  for  the  tubing.  The  tubing  is  more  easily 
inserted  if  it  is  moistened.  If  the 
hole  in  the  cork  is  too  small,  there 
is  danger  of  breaking  the  tubing 
and  seriously  cutting  the  hands. 
Rubber  corks  with  holes  in  them 
are  now  so  easily  obtained  that  they  should  be  used  when 
possible. 

Heating  Liquids  in  Test  Tubes.  Hold  the  test  tube  by 
means  of  a  test  tube  holder  or  a  band 
of  paper  as  in  Fig.  14.  Heat  writh  the 
point  of  the  flame  near  the  top  of  the 
liquid,  but  do  not  allow  the  flame  to 
strike  the  glass  above  the  liquid. 
Agitate  slightly  during  heating.  Be 
careful  that  the  mouth  of  the  test  tube 
does  not  point  toward  any  one  in  case 
the  vapor  forces  the  liquid  out  of  the 
tube. 

When  heating  liquids  in  glass  beakers 
FIQ.  14.  the  same  precaution  must  be  observed 


FIQ.  13. 


INTRODUCTORY  LABORATORY  MANIPULATIONS     15 


against  allowing  the  flame  to  strike  the  glass  above  the 
liquid.  Beakers  should  be  protected  by  placing  them  on 
a  piece  of  wire  gauze  or  asbestos  board  (Fig.  15).  In  some 


FIG.  15. 


FIG.  16. 


cases  it  is  desirable  to  use  a  sand  bath,  which  consists  of  a 
small  pan  containing  sand  (Fig.  16).  This  distributes  the 
heat  evenly  and  prevents  breakage. 

Evaporation  is  commonly  performed  in  small  porcelain 
evaporating  dishes 
(Fig.  17).  Wire 
gauze  or  the  sand 
bath  is  frequently 
used  with  the 
evaporating  dishes. 
If  the  substance  is 
injured  by  high 


temperature,    it    is 

evaporated  over  a 

water  bath  (Fig.  18),  in  which  case  the  evaporating  dish  is 

heated  by  the  steam  of  the  boiling  water.     The  double 


FIG.  17. 


FIG.  18. 


EV.  CHEM. — 2 


16    INTRODUCTORY   LABORATORY  MANIPULATIONS 


boiler  is  an  example  of  the  practical  use  of  a  water  bath  in 
the  home. 

Filtration  is  used  to  separate  a  solid  from  a  liquid  sub- 
stance. It  is  usually  performed  by  filtering  the  liquid 
through  a  specially  prepared 
paper  known  as  filter  paper. 
This  comes  in  circular  pieces  in 


FIG.  19. 


FIG.  20. 


various  sizes,  which  are  folded  as  shown  in  Fig.  19  so  as  to  fit 
into  a  glass  funnel  (Fig.  20) .  When  poured  on  the  filter  paper 
the  liquid  runs  through,  while  the  solid  remains  in  the  funnel. 
In  transferring  liquids  from  one  vessel  to  another  it  is 
best  to  pour  the  liquid  down  a  glass  rod  (Fig.  20)  as  this 
prevents  danger  of  loss  of  the  substance  by 
splashing.  Direct  the  stream  against  the 
side  of  the  beaker  or  other  vessel  to  which 
the  liquid  is  being  transferred.  When 
pouring  into  a  filter  direct  the  stream 
against  the  side  of  the  filter  having  the 
three  layers  of  paper. 

Keep  the  reagents  pure  by  using  ex- 
treme care  to  prevent  contamination  of  any  kind.  Do 
not  lay  the  stopper  on  the  desk,  but  take  it  from  the  bottle 


FIG.  21. 


INTRODUCTORY  LABORATORY  MANIPULATIONS     17 


FIG.  22. 


as  shown  in  Fig.  21,  holding  both  the  bottle  and  the 
stopper  in  the  fingers  as  indicated  in  Fig.  22.  Never  pour 
any  liquid  back  into  the  reagent 
bottle.  A  very  little  foreign  sub- 
stance in  a  reagent  may  spoil  a 
future  experiment.  Use  small  quan- 
tities of  all  reagents.  Many  ex- 
periments are  ruined  by  the  use  of 
too  much  material. 

To  collect  gases  the  pneumatic  trough  is  used  (Fig.  23). 
Any  deep  pan  will  serve  the  purpose.     The  bottle  used  to 

collect  the  gas  is  filled 
with  water  and  placed 
mouth  downward  in  the 
pneumatic  trough.  The 
bottle  is  slightly  tilted 
so  that  the  gas  may  enter 
FIG.  23.  at  A  and  displace  the 

water  in  the  bottle.  Ex- 
periment in  collecting  gases  by  placing  a  piece  of  tubing 
under  the  bottle,  as  shown  in  the  illustration,  and  gently 
blowing  into  it.  To  remove  the  bottle  of 
gas  from  the  trough  slip  a  small  piece  of 
window  glass  beneath  the  mouth  of  the 
bottle  (Fig.  24)  while  it  is  still  under 
water.  If  the  gas  is  heavier  than  air,  the 
bottles  should  be  stored  mouth  upward 
with  the  glass  plate  on  top.  If  the  gas 
is  lighter  than  air,  the  bottles  are  kept 
mouth  downward. 

Some  gases  are  so  soluble  in  water  that  some  other  method 
than  the  one  described  above  must  be  used  in  collecting 


FIG.  24. 


18     INTRODUCTORY   LABORATORY  MANIPULATIONS 


FIG.  25. 


them.  They  may,  in 
many  cases,  be  collected 
over  mercury,  but  the 
method  more  commonly 
used  in  the  laboratory  is 
by  displacement  of  air. 
The  gas  is  allowed  to  run 
into  the  collecting  vessel 
until  it  has  driven  out  all 
or  practically  all  of  the 
air.  When  the  gas  is 
heavier  than  air  it  is  col- 
lected by  downward  dis- 
placement (Fig.  25).  If  lighter  than  air,  the  gas  is  collected 
by  upward  displacement  (Fig.  26). 

Cleanliness  is  abso- 
lutely necessary  to  suc- 
cessful laboratory  work. 
All  apparatus  should  be 
clean  before  use,  and 
should  be  washed  as  soon 
as  the  experiment  has 
been  completed.  Direc- 
tions should  be  carefully 
followed  in  all  the  experi- 
ments, and  no  exercise 
should  be  started  until 
the  entire  procedure  is 
thoroughly  understood  by 
the  student.  FIG.  26. 


CONTENTS 

INTRODUCTORY  LABORATORY  MANIPULATIONS 


PAGE 

11 


PART  I:    INORGANIC  CHEMISTRY 

CHAPTER 

I.  WATER 21 

II.  WATER  (Continued} 34 

III.  HYDROGEN 45 

IV.  OXYGEN 52 

V.  OXYGEN  (Continued] 61 

VI.  AIR  —  NITROGEN 70 

VII.  SULPHUR 78 

VIII.  THE  ATOMIC  THEORY 91 

IX.  FORMULAS  AND  EQUATIONS.     .        .        .        .        .97 

X.  Acros  OF  SULPHUR  AND  HYDROGEN  SULPHIDE       .  104 

XI.  CARBON Ill 

XII.  CARBON  COMPOUNDS 123 

XIII.  LIMESTONE  AND  OTHER  CALCIUM  COMPOUNDS        .  134 

XIV.  SALT:   CHLORINE  AND  SODIUM        ....  144 
XV.  ACIDS,  BASES,  AND  SALTS 154 

XVI.  NITRIC  ACID  AND  OXIDES  OF  NITROGEN         .        .161 

XVII.  AMMONIA  AND  ITS  COMPOUNDS        .        .        .        .171 

XVIII.  PHOSPHORUS,  PHOSPHORIC  Aero,  AND  ARSENIC       .  184 

XIX.  SAND,  SILICON,  AND  BORAX 193 

XX.  RECOGNITION  OF  SUBSTANCES 201 

XXI.  POTASSIUM 204 

XXII.  MAGNESIUM  AND  ZINC 210 

XXIII.  ALUMINUM 214 

XXIV.  IRON 220 

XXV.  LEAD 226 

XXVI.  COPPER 230 

XXVII.  SILVER 235 

XXVIII.  REVIEW  OF  THE  METALLIC  SALTS  —  RECOGNITION 

OF  THE  COMMON  METALS        ,  240 
19 


20 


CONTENTS 


PART 

CHAPTER 

XXIX. 
XXX. 

II:   ORGANIC  AND  APPLIED  CHEMISTRY 
COMPOUNDS  OF  CARBON  WITH  HYDROGEN 

PAGE 

244 
250 

XXXI. 

ORGANIC  ACIDS        , 

256 

XXXII. 

FATS,  OILS,  AND  SOAPS  ....... 

263 

XXXIII. 

CARBOHYDRATES       ....... 

270 

XXXIV. 

ORGANIC  NITROGEN  COMPOUNDS     . 

280 

XXXV. 

COMPOSITION  OF  PLANTS          ..... 

289 

XXXVI. 

CHEMISTRY  OF  PLANT  GROWTH       .... 

298 

XXXVII. 

CHEMISTRY  OF  PLANT  GROWTH  (Continued)    . 

309 

XXXVIII. 

ENZYMES  —  DIGESTION  —  FERMENTATION 

317 

XXXIX. 

PRINCIPLES  OF  NUTRITION       

324 

XL. 

FEEDING  FARM  ANIMALS          ..... 

331 

XLI. 

HUMAN  FOODS         

341 

XLII. 

MILK  AND  ITS  PRODUCTS         . 

350 

XLIII. 

TESTING  MILK         ....... 

364 

XLIV. 

LEAVENING  AGENTS         ...... 

375 

XLV. 

FOOD    PRESERVATION,    ANTISEPTICS,    AND    DISIN- 

FECTANTS   

384 

XLVI. 

TEXTILES,  DYEING,  AND  BLEACHING 

392 

XLVIL 

PAINTS  AND  VARNISHES  ....... 

399 

XLVIII. 

CLEANING  MATERIALS     ...... 

404 

XLIX. 

INSECTICIDES  AND  FUNGICIDES 

411 

PART  III:    SOILS  AND  FERTILIZERS 

L. 

SOIL  FORMATION      

420 

LI. 

KINDS  OF  SOILS       .        

426 

LII. 

RELATION  OF  THE  SOIL  TO  PLANTS 

433 

LIII. 

SOIL  WATER    ........ 

440 

LIV. 

TILLAGE   ......... 

455 

LV. 

KEEPING  THE  SOIL  SWEET      .                 .        .        . 

473 

LVI. 

ORGANIC  MATTER    ....... 

485 

LVII. 

ROTATION  OF  CROPS        

495 

LVIII. 

STABLE  MANURE      .        . 

501 

LIX. 

COMMERCIAL  SOURCES  OF  PLANT  FOOD  . 

520 

LX. 

MIXED  FERTILIZERS         

533 

LXI. 

TYPES  OF  FARMING  AND  FERTILITY 

542 

APPENDIX 

TABLES    ......... 

549 

INDEX       ....0,0.. 

553 

PART   I 

INORGANIC   CHEMISTRY 

CHAPTER  I 

WATER 

1.  WATER  moves  in  an  unending  cycle.     The  heat  of  the 
sun  evaporates  the  water  from  the  surface  of  rivers,  lakes, 
and  oceans.     The  moisture  thus  added  to  the  atmosphere 
remains  as  water  vapor  until  the  air  is  cooled ;  then  it  ap- 
pears first  as  clouds,  and  finally  is  precipitated  as  rain.      The 
rain  water   soaks  into  the  soil,  later  appears   in   springs, 
rivers,  and  lakes,  and  is  eventually  returned  to  the  ocean  only 
to  repeat,  over  and  over  again,  this  unceasing  round  of 
changes. 

2.  Water  Never  Pure  in  Nature.     While  water  is  very 
abundant,  it  is  never  found  in  a  pure  state  in  nature.     As 
it  soaks  into  the  soil  it  dissolves  many  of  the  mineral  sub- 
stances found  therein,  and,  as  a  result,  the  water  issuing  in 
the  springs  and  rivers  contains  dissolved  mineral  matter, 
which  is  carried  with  it  to  the  ocean.    'When  water  evapo- 
rates, the  dissolved  solids  remain,  and,  consequently,  sea 
water  contains  relatively  large  quantities  of  dissolved  mat- 
ter.    All  the  salt  and  other  mineral  matter  found  in  sea 
water,  therefore,  was  originally  dissolved  from  the  soil  and 
carried,  by  the  streams  to  the  ocean.     That  the  water  of 
wells,  springs,  or  rivers  contains  dissolved  substances  may 

21 


22 


INORGANIC  CHEMISTRY 


FIG.  27.  — Evaporating  water  to 
show  the  presence  of  dissolved 
mineral  matter. 


easily  be  shown  by  evaporating  a  small  quantity  to  dryness 
in  a  porcelain  evaporating  dish,  as  illustrated  in  Fig.  27. 

If  like  amounts  of  water  from 
various  sources  are  evaporated,  it 
will  be  found  that  there  is  a  great 
variation  in  the  amount  of  solid 
substance  left  in  the  evaporating 
dishes.  The'  nature  of  the  ma- 
terials obtained  from  well  and 
spring  water  depends,  evidently, 
upon  the  character  of  the  rock 
and  soil  in  which  the  well  or 
spring  is  located.  Granite  rocks 
are  very  insoluble,  while  lime- 
stone is  much  more  readily  dis- 
solved. Water  issuing  from  the  former  contains  very  little 
dissolved  substance,  whereas  it  is  a  well-known  fact  that 
the  water  in  limestone  regions  is  heavily  charged  with 
mineral  matter. 

3.  Rain  Water  the  Purest  Natural  Water.     The  purest 
natural  water  is  rain  water,  but  even  that  is  not  perfectly 
pure.     The  atmosphere  always  contains  more  or  less  dust 
and  smoke,  and  when  rain  falls  it  carries  these  substances 
down  with  it.     Rain  water  in  the  open  country  is  purer  than 
that  in  or  near  the  cities,  and  if  the  water  is  not  collected 
until  the  air  has  been  washed  by  the  rain  for  some  minutes, 
comparatively  pure  water  may  be  obtained. 

4.  Distillation  of  Water.       Pure  water  is  obtained  by 
boiling  well  water  or  hydrant  water  and  condensing  the 
steam.     This  process  is  known  as  distillation  and  may  con- 
veniently be  carried  out  in  the  apparatus  shown  in  Fig.  28. 
The  water  is  boiled  in  the  flask  A,  and  the  steam  passing 


WATER 


23 


into  the  inner  tube  of  the  condenser  B  is  cooled  and  changed 
back  to  water,  which  is  collected  in  the  receiving  flask  C. 
A  current  of  cold  water  is  kept  running  through  the  con- 
denser, entering  at  D  and  flowing  out  at  E.  This  water 
cools  the  inner  tube  of  the  condenser  sufficiently  to  cause 


FIG.  28.  —  Apparatus  for  the  distillation  of  water. 

the  condensation  of  the  steam  entering  from  the  flask  A. 
The  water  which  collects  in  C  is  known  as  distilled  water 
and  is  quite  pure,  since  the  impurities  of  the  original  water 
remain  in  the  boiling  flask.  The  first  fifty  cubic  centime- 
ters which  pass  over  should  be  rejected,  as  gases  and  other 
volatile  substances  may  distill  over  with  the  first  portions 
of  water,  and  the  inside  of  the  condenser  may  not  be  en- 
tirely free  from  soluble  materials.  If  proper  precautions 
have  been  observed,  the  distilled  water  made  in  this  way 
will  leave  no  residue  when  evaporated  in  a  porcelain  dish. 

5.  Properties  of  Water.  Pure  water  is  tasteless  and 
odorless.  In  small  quantities  it  seems  to  be  colorless,  but 
when  viewed  in  deep  layers  it  becomes  apparent  that  it  has 


24  INORGANIC  CHEMISTRY 

a  blue  color.  This  is  illustrated  in  the  beautiful  blue  color 
of  many  mountain  lakes,  which  consist  of  almost  pure 
water  derived  from  the  melting  snow. 

6.  Three  States  of  Water.  When  water  is  boiled  it  is 
gradually  changed  into  a  colorless  and  invisible  vapor, 
which,  upon  cooling,  is  again  converted  into  liquid  water. 
If  the  vapor  escapes  into  the  cooler  air,  it  is  partially  con- 
densed and  forms  what  is  popularly  known  as  steam.  That 
true  steam,  or  water  vapor,  is  invisible  can  be  shown  by 
boiling  water  in  a  flask.  It  will  be  found  that  nothing  can 
be  seen  in  the  upper  part  of  the  flask  although  it  must  be 
full  of  steam.  It  is  only  as  the  steam  escapes  into  the  air 
and  is  condensed  to  small  droplets  of  water  that  it  can  be 
seen. 

Most  substances  contract  when  they  are  cooled.  Water 
when  cooled  follows  the  general  rule  to  four  degrees  centi- 
grade, whereupon  it  begins  to  expand.  At  4°  C.  water 
reaches  its  maximum  density.  At  the  moment  the  water 
freezes,  a  considerable  increase  in  volume 
takes  place,  and  the  resulting  ice  has  a 
density  not  much  more  than  nine  tenths 
that  of  the  water  from  which  it  was  formed. 
This  explains  why  ice  is  always  found  on  top 
of  the  water.  If  the  volume  contracted  as 
freezing  took  place,  ice  would  sink  to  the 
bottom,  and  the  lakes  and  rivers  would  be 
frozen  to  a  solid  mass  of  ice.  This  expansion 

FIG.  29.— Bot-         f  ,-.  p          '  i  f 

tie  broken  by  the  of  the  water  upon  ireezing  also  accounts  tor 
omtaiiJed vnter*  the  fact  that  ice  is  always  pushed  up  on  the 
banks  of  the  lakes  and  rivers.  The  great  force 
exerted  by  the  expansion  of  water  at  the  moment  of  freezing 
is  well  known,  and  nearly  every  one  can  recall  an  experience 


WATER 


25 


with  the  bursting  of  a  water  pipe,  a  bottle  (Fig.  29),  a  bucket 
or  of  some  other  vessel,  due  to  the  freezing  of  the  con- 
tained water.  This  force  is  also  an  important  factor  in  the 
weathering  of  rocks  and  in  the  formation  of  soils  (483) . 

7.   Water  used  to  Establish  Standards.      Pure  water  is 
used  to  establish  many  of  the  scientific  standards  of  measure- 
ment.    The  two  fixed  points  of  the  ther- 
mometer are  the  boiling  and  the  freezing 
points  of  water.     To  graduate  a  thermome- 
ter the  bulb  is  placed  in  melting  ice,  and  the 
height    of    the    mercury    is    marked.     This 
point  is  the  zero  of  the  centigrade  scale,  or 
thirty-two  degrees  on    the   Fahrenheit    scale 
(Fig.   30).      The  thermometer  is   then  im- 
mersed in  boiling  water  and  the  height  of 
the   mercury  again  marked.     This  point  is 
marked  100  degrees  centigrade,  or  212  degrees 
Fahrenheit.     The  space  between  these  marks 
is  then  divided  into  one  hundred  equal  spaces 
for  the  centigrade  scale  and  into  180  for  the 
Fahrenheit.     Since  the  boiling  and  the  freez- 
ing points  of  liquids  vary  with  the  atmos- 
pheric   pressure,    the    graduation   described 
above  must  be  made  at  sea  level,  or  be  cor- 
rected for  the   difference   in  pressure.     In- 
creased pressure  raises  the  boiling  point  and 
lowers  the  freezing  point,  while  decreased  pressure  has  the 
opposite  effect.     That  water  under  decreased  pressure  boils 
at  a  lower  temperature  can  readily  be  shown  by  boiling  water 
in  a  flask  closed  with  a  two-hole  rubber  cork,  in  one  hole 
of  which  is  placed  a  thermometer,  and  in  the  other  a  tube 
that  is  connected  with  an  air  pump  (Fig.  31).     If  the  air  is 


A        B 

FlQ.  30. —Fah- 
renheit (A )  and 
centigrade  (B) 
thermometers 
showing  the  rela- 
tion of  the  scales. 


INORGANIC  CHEMISTRY 


partially  exhausted  from  the  flask,  the  water  will  be  found  to 
boil  much  below  100°  C.     The  same  result  may  be  obtained 


FIG.  31.  —Apparatus  to  show  effect  of  reduced  pressure  on  boiling  point  of  water. 

by  heating  water  in  a  flask,  and,  while  the  water  is  boiling 
hard,  closing  the  flask  with  a  rubber  stopper,  and  removing 
the  flask  from  the  flame.  If  now  a  stream  of  water  is  run 

over  the  upper  part  of  the  flask 
(Fig.  32),  the  steam  will  be  con- 
densed, a.  partial  vacuum  will  be 
produced,  and  the  water  will  again 
boil.  This  may  be  continued 
until  the  temperature  of  the  water 
is  much  below  its  normal  boiling 
point.  On  the  top  of  Pikes  Peak 
water  boils  at  such  a  low  tempera- 
ture that  an  egg  cannot  be  cooked 
hard  in  it. 
FIG.  32. —A  simple  way  of  The  gram,  the  standard  of 

showing  the  effect  of  reduced  pres-  .    -.  ,        »    ,  -. 

sures  on  the  boiling  point.  weight  ot  the  metric  system,  is 


WATER 


the  weight  of  one  cubic  centimeter  of  water  at  its  maximum 
density ;  that  is,  at  4°  C.  Water  is  also  used  as  a  standard 
of  density ;  for  the  relative  density,  or  specific  gravity,  of  any 
substance  is  determined  by  dividing  its  weight  by  that  of 
an  equal  volume  of  water.  The  standard  for  the  measure- 
ment of  a  quantity  of  heat  is  the  calorie,  which  is  the  amount 
of  heat  required  to  raise  the  temperature  of  one  gram  of 
water  1°  C.  This  is  sometimes  called  the  small  calorie. 
The  large  calorie  is  the  amount  of  heat  required  to  raise 
1000  grams  of  water  1°  C. 

8.  Heat  of  Fusion  and  Vaporization.  When  ice  is  heated 
it  melts,  but  if  a  thermometer  is  placed  in  the  melting  ice 
(Fig.  33),  and  the  mass  is  kept  thoroughly  stirred,  it  will  be 
found  that  the  temperature  of  the 
mass  does  not  rise  until  all  the  ice 
has  been  melted.  Although  much 
heat  has  been  applied,  it  has  all 
been  used  to  melt  the  ice  and  not 
to  raise  the  temperature.  The 
heat  required  merely  to  melt  a 
substance  is  termed  heat  of  fusion. 
When  the  water  freezes,  the  same 
amount  of  heat  is  given  off.  Simi- 
larly a  large  amount  of  heat  is 
required  to  change  water  into 
vapor,  or  steam,  and  this  is  known 
as  the  heat  of  vaporization  of  the 

water.  Whenever  water  evaporates  it  absorbs  an  amount  of 
heat  equal  to  its  heat  of  vaporization  and,  consequently, 
cools  both  the  air  in  the  vicinity  and  the  surface  from  which 
evaporation  takes  place.  This  explains  why  sprinkling  the 
floor  on  a  hot  day  cools  the  room.  In  India,  wet  cloths  are 


FIG.  33. — The  temperature  of 
the  water  does  not  rise  until  all 
the  ice  is  melted. 


28 


INORGANIC  CHEMISTRY 


frequently  hung  in  doorways,  so  that  the  air  entering  the 
house  will  be  cooled  by  evaporation  of  the  water.  Drink- 
ing water  in  hot 
climates  is  often 
stored  in  semi- 
porous  earthenware 
jars  (Fig.  34)  in 
order  that  the  water 
oozing  through  may 
evaporate  from  the 
surface  and  thus 
cool  the  jar  and  its 
contents. 

9.  Water  a  Poor 
Conductor  of  Heat. 
It  may  be  shown 
that  water  is  a  poor 
conductor  of  heat 
by  applying  heat  to 

the  top  of  a  test  tube  full  of  water  (Fig.  35) .  The  water  in 
the  upper  portion  of  the  tube  can  be  made  to  boil  while  the 
bottom  is  still  cool.  To  raise  the  temperature  of  a  large  body 
of  water  it  is  necessary  to  apply  heat  at  the  bottom.  When 
the  water  next  to  the  fire  becomes  heated,  it  expands,  be- 
comes less  dense,  and  rises  to  the  top  (Fig.  36) .  The  cooler 
and  heavier  liquid  streams  down  to  replace  it,  and  thus  a 
system  of  currents  is  set  up  that  gradually  distributes  the 
heat  throughout  the  whole  mass.  This  statement  applies  to 
other  liquids  and  to  gases  as  well  as  to  water. 

An  interesting  series  of  changes  takes  place  when  a  pond 
or  other  body  of  water  freezes  over.  As  the  air  above  the 
water  becomes  colder,  heat  is  given  off  from  the  surface  of 


FIG.  34.  — Semi-porous  water  jars  on  sale  in  a 
bazaar  in  Allahabad,  India. 


WATER 


29 


FIG.  35.  —  Showing  that  water  is 
a  poor  conductor  of  heat. 


the  water,  and  the  cold  water  from  above  streams  down  to 

the  bottom  of  the  pond  and  forces  the  warmer  water  to  come 

to  the  surface.      This  continues 

until  all  the  water  in  the  pond 

is  cooled  to  4°  C.     Upon  further 

cooling  the  water  at  the  surface 

expands,  thus   becoming  lighter, 

and  no  longer  moves  downward. 

When  the  surface  is  cooled  to  0° 

C.,  the  water  freezes,  giving  off  an 

amount  of  heat  equal  to  its  heat 

of  fusion,  and   the  temperature 

of  the  water  immediately  below 

the  ice  is  temporarily  raised.    The 

layer  of  ice  increases  in  thickness 

due  to  the  loss  of  heat  from  the  surfa:e  until  it  is  sufficiently 

thick  to  prevent  further  radiation  of  heat  from  the  water 

beneath,  ice  being  a  relatively 
poor  conductor  of  heat.  It  thus 
happens  in  deep  ponds  that  the 
water  at  the  bottom  does  not  fall 
to  the  freezing  point,  even  in  very 
cold  weather. 

10.  Water  Has  High  Specific 
Heat.  Water  requires  more  heat 
to  make  it  hot  than  does  any  other 
substance.  If  equal  amounts  of 
heat  are  applied  to  equal  masses 
of  water  and  mercury,  for  in- 
stance, the  mercury  gets  hot  much 

more  rapidly  than  the  water.     Water,  therefore,  is  said  to 

have  a  greater  capacity  for  heat,  or  a  greater  specific  heat, 


FIG.  36.  —  Currents  of  warm 
water  move  upward  as  the  bottom 
layers  are  heated. 


30 


INORGANIC  CHEMISTRY 


than  other  substances.  This  property  of  water  is  of  im- 
portance, for  substances  that  heat  slowly  also  cool  slowly. 
This  is  one  reason  why  hot  water  and  steam  are  used  to  heat 
houses,  and  explains  why  large  bodies  of  water  have  a 
moderating  effect  upon  the  climate  of  their  vicinity. 


EXERCISES 

Ex.  1.  Evaporate  10  cc.  each  of  well  water  and  rain  water  to  dry- 
ness  by  heating  in  glass  dishes  or  watch  glasses  on  a  sand  bath  (Fig.  37). 

What  remains  in  the  dish?  Which 
water  gave  the  larger  residue  ?  Which 
sample  of  water  was  the  purer  ?  Was 
either  one  perfectly  pure?  How  did 
the  residue  in  the  dish  get  into  the 
water?  From  which  well  should  you 
expect  the  most  residue,  one  located 
in  granite,  sandstone,  or  limestone? 
Why?  Why  does  sea  water  contain 
large  quantities  of  salt  and  other  min- 
eral matter?  Where  does  the  mineral 
matter  in  sea  water  come  from  ?  Ex- 
plain the  cycle  of  water  in  nature. 

Ex.  2.  Arrange  an  apparatus  ac- 
cording to  Fig.  28.  Half  fill  the  flask 
A  with  the  well  water  used  in  Ex.  1 

and  boil  until  50  cc.  of  water  is  collected  in  C.  Evaporate  10  cc.  of 
the  distilled  water  to  dryness  as  above.  Is  there  any  residue  ?  Com- 
pare with  the  well  water  before  distillation.  What  has  become  of 
the  mineral  matter  that  was  in  the  well  water  ?  How  is  pure  water 
obtained  ? 

(Note.  If  the  condenser  shown  in  Fig.  28  is  not  available,  sufficient 
distilled  water  for  this  test  can  be  produced  with  the  apparatus  shown  in 
Fig.  38.  Surround  the  test  tube  with  the  coldest  water  obtainable. 
If  ice  is  available  to  cool  this  water,  more  distilled  water  can  be  pro- 
duced.) 


FIG.  37..  —  Evaporating  a  small 
quantity  of  water  on  a  watch 
glass. 


WATER 


31 


FIG.  38.  — A  simple  apparatus  for 
producing  a  small  quantity  of  distilled 

water. 


Ex.  3.  Add  a  few  crystals  of  copper  sulphate  to  the  water  in  flask 
A  and  distil  a  few  cubic  centimeters  of  water.  What  is  the  color  of  the 
water  in  the  flask  A  ?  What  is  the 
color  of  the  distilled  water  (some- 
times called  the  distillate)  ?  Explain 
the  difference.  In  producing  pure 
distilled  water  why  should  the  first 
water  that  distilled  over  be  rejected  ? 
State  the  properties  of  pure  water. 

Ex.  4.  Boil  some  water  in  a  flask 
which  is  open  at  the  top.  Is  the 
vapor  in  the  upper  part  of  the  flask 
visible?  Why  does  the  "steam" 
become  visible  when  the  vapor 
passes  into  the  air?  Use  a  ther- 
mometer to  determine  the  tempera- 
ture of  the  water  vapor  (Fig.  39). 

Ex.  6.     If  the  weather  is  sufficiently  cold,  place  a  bottle  full  of 
water  out  of  doors  to  freeze.     Does  water  contract  when  cooled? 

What  happens  when  the  water  freezes  ? 
Why  does  ice  float  on  top  of  the  water  ? 
What  would  happen  to  lakes  if  ice 
were  heavier  than  water?  At  what 
temperature  is  water  at  its  maximum 
density  ? 

Ex.  6.  Boil  water  in  a  partial 
vacuum  created  by  an  air  pump,  as 
suggested  in  the  text.  At  what  tem- 
perature does  the  water  boil  ?  At  what 
temperature  did' it  boil  in  Ex.  4?  Ex- 
plain the  difference.  What  is  the  ele- 
vation of  your  school  above  sea  level  ? 
Should  you  expect  water  to  boil  in  your 
laboratory  at  100°  C.  or  below  ?  Why  ? 
.  Ex.  7.  Fit  a  flask  with  a  good  rub- 
ber stopper  and  place  in  the  stopper 
Attach  a  piece  of  rubber  tubing  and  a 
Boil  the  water  in 


FIG.  39. — Determining  the  tem- 
perature of  water  vapor.' <•$$>& 


a  short  piece  of  glass  tubing-. 

pinchcock  to  the  upper  end  of  the  glass  tubing. 


32 


INORGANIC  CHEMISTRY 


the  flask  until  all  air  is  driven  out,  and  while  the  water  is  still  boiling 
close  the  pinchcock  and  immediately  remove  the  flame.  Now  run  cold 
water  over  the  upper  part  of  the  flask.  Explain  what  happens  to  th'3 
water  in  the  flask.  Why  does  it  take  longer  to  cook  vegetables  by  boil- 
ing at  high  altitudes  than  at  sea  level  ?  If  the  flask  used  in  this  exercise 
were  strong  enough  to  risk  boiling  the  water  after  the  cork  was  inserted, 
would  the  boiling  point  of  the  water  be  raised  or  lowered  ?  Why  ? 

Ex.  8.  Place  a  beaker  or  tin  cup  of  water  over  a  burner  and  watch 
the  rise  of  temperature  of  the  water  by  means  of  a  thermometer.  Does 
the  temperature  begin  to  rise  immediately?  Try  the  experiment 
again,  using  water  with  ice  in  it.  Does  the  tem- 
perature rise  immediately  in  this  case  ?  Explain 
the  difference. 

Ex.  9.  Cool  a  pound  of  water  (1  pint)  to  zero 
by  immersing  the  vessel  in  a  mixture  of  ice  and 
salt  until  the  desired  temperature  is  reached; 
then  remove  from  the  cooling  mixture.  Have 
another  pint  of  water  heated  to  80°  and  pour  into 
the  water  at  zero.  Stir  it  quickly  with  the  ther- 
mometer and  read  the  temperature.  What  is  the 
temperature  of  the  mixture? 

Weigh  one  pound  of  ice  and  pour  over  it  a  pint 
of  water  which  has  been  warmed  to  80°.  Stir 
and  read  the  temperature  as  soon  as  the  ice  has 
melted.  What  is  the  temperature  in  this  case? 
How  do  you  explain  the  difference  in  the  two 
parts  of  this  exercise?  (Note  that  the  ice  used 
in  this  experiment  must  be  at  0°  C.  Can  ice 
be  colder  than  zero  ?  If  all  conditions  are  right 
for  the  above  experiment,  the  mixture  of  water 
at  80°  and  water  at  zero  will  have  a  temperature 
of  40°,  while  the  mixture  of  water  at  80°  and  ice  at  zero  will  have  a 
temperature  of  zero.  Eighty  times  as  much  heat  is  required  to  melt 
a  pound  of  ice  as  is  required  to  warm  a  pound  of  water  one  degree.) 
What  is  meant  by  heat  of  fusion?  What  becomes  of  the  heat  of 
fusion  when  the  water  freezes?  When  there  is  danger  of  freezing  it 
is  sometimes  suggested  that  a  tub  of  water  be  placed  in  the  cellar. 
What  is  the  theory  of  this  recommendation  ? 


FIG.  40.  —  Wet  and 
dry  bulb  thermome- 
ters to  show  the  effect 
of  evaporation  on  the 
temperature. 


WATER  33 

Ex.  10.  Compare  two  thermometers  to  see  that  they  register  alike. 
Wrap  a  piece  of  thin  cloth  around  the  bulb  of  one  and  moisten  it  with 
water  (Fig.  40).  Fan  the  two  thermometers  and  observe  the  change  in 
temperature  registered.  Is  there  any  difference  in  the  two  thermome- 
ters ?  Explain.  Why  does  sprinkling  the  floor  lower  the  temperature  of 
the  room  ?  Explain  the  use  of  porous  jars  to  cool  water  in  hot  climates. 
Can  you  think  of  any  other  instance  of  the  cooling  effect  of  evaporating 
water  ? 

Ex.  11.  Fill  a  long  test  tube  with  water  and  heat  the  upper  part 
over  a  burner  until  the  water  boils.  Is  the  lower  part  of  the  tube  hot  ? 
How  do  you  explain  it?  Where  should  the  heat  be  applied  to  warm 
water  with  the  least  fuel  ?  Explain.  Explain  the  changes  that  take 
place  in  the  freezing  over  of  a  pond.  What  is  meant  by  specific 
heat?  How  does  the  specific  heat  of  water  compare  with  that  of 
other  substances  ?  Is  there  any  connection  between  this  fact  and  the 
use  of  hot  water  and  steam  in  heating  buildings  ?  Explain  the  moder- 
ating effect  which  large  bodies  of  water  have  upon  climate. 


EV.  CHEM. — 3 


CHAPTER  II 


WATER    (Continued) 

11.  Water  the  Best  Solvent.  Water  is  the  best-known 
solvent.  In  other  words,  it  will  dissolve  more  substances 
than  any  other  liquid.  There  are  some  substances,  how- 
ever, which  are  insoluble  in  water.  Substances  vary  greatly 
in  solubility,  ranging  from  those  which  will  dissolve  in  a 
fraction  of  their  own  weight  of  water,  to  those  whose  solu- 
bility can  scarcely  be  detected.  Water  dissolves  other 

liquids  and  gases  as  well  as  solid 
substances.  Liquids  which  are 
soluble  in  water  are  said  to  be 
miscible  with  water.  Alcohol  is 
miscible  with  water  in  all  pro- 
portions, and  so  is  sulphuric  acid. 
Oils,  on  the  other  hand,  are  prac- 
tically insoluble  in  water.  The 
fact  that  air  and  other  gases  are 
dissolved  in  natural  waters  can 
be  shown  by  gently  heating  the 
water  in  a  glass  vessel  (Fig.  41), 
whereupon  bubbles  of  gas  will  be 
seen  to  separate.  The  solubility  of  substances  in  water  is 
affected  by  temperature.  As  a  general  rule,  the  solubility 
of  solids  increases  with  the  rise  of  temperature,  while  that 
of  gases  decreases.  Increase  of  pressure  has  a  very  marked 
effect  upon  the  solubility  of  gases  in  water,  for  the  amount 

34 


Flo.  41 .  —  Warming  water  to  show 
the  presence  of  dissolved  gases. 


WATER  35 

of  gas  dissolved  is  directly  proportional  to  the  pressure; 
that  is,  if  the  pressure  upon  the  gas  is  doubled,  twice  as  much 
will  be  dissolved  by  the  water. 

12.  Dissolved   Substances   Raise   the   Boiling  Point  of 
Water.      Substances  dissolved  in  water  raise    its  boiling 
point  and  lower  its  freezing  point.     Water  in  which  salt 
is  dissolved,  for  instance,  has  to  be  heated  above  100°  C.  be- 
fore it  will  boil,  and  it  will  not  freeze  until  much  below 
0°  C.     This  effect  of  the  dissolved  substance  is  made  use  of 
in  a  number  of  practical  ways,  some  of  which  will  be  re- 
ferred to  later.     When  the  water  contains  all  of  the  sub- 
stance it  can  dissolve,  the  solution  is  said  to  be  saturated. 
From  what  has  been  said  above  it  will  be  seen  that  a  solu- 
tion which  is  saturated  at  a  low  temperature  will  no  longer 
be  saturated  if  the  temperature  is  raised,  and  that  more  of 
the  substance  may  then  be  dissolved.     Conversely,  if  the 
temperature  of  a  saturated  solution  is  lowered,  some  of  the 
dissolved  substance  will  be  thrown  out  of  the  solution. 

13.  Water  Accelerates  Chemical  Action.     Water  is  also 
of  interest  to  the  chemist  because  it  hastens  chemical  changes. 
In  fact,  most  of  the  important  chemical  changes  will  not 
take  place  at  all  in  the  absence  of  water.     If  a  small  quan- 
tity of  dry  baking  soda  and  dry  powdered  tartaric  acid  are 
mixed  in  a  beaker,  no  change  will  take  place.     If,  however, 
a  little  water  is  added,  a  marked  change  takes  place,  the 
most  noticeable  thing  being  the  large  amount  of  gas  that  is 
evolved.     The  rusting  of  iron  is  another  example  of  a  chemi- 
cal change  which  occurs  only  in  the  presence  of  moisture. 

14.  Potable  Waters.     What  is   popularly  meant    by  a 
pure  water  is  one  that  is  fit  to  use  for  drinking  purposes. 
Such  a  water  is  technically  called  a  potable  water.    Sea  water 
with  its  large  amount  of  salt  is  obviously  unfit  to  drink,  but 


36 


INORGANIC  CHEMISTRY 


it  is  seldom  indeed  that  the  mineral  substances  found  in  well 
or  spring  water  are  injurious.  The  chief  source  of  danger  in 
drinking  water  is  that  it  may  be  contaminated  (Fig.  42) 

with  sewage,  if  the 
source  of  the  water 
is  near  human  habi- 
tations. The  water 
from  cesspools  may 
enter  the  well  or 
spring,  or  the  city 
sewage  may  be 
emptied  into  the 
river.  In  either  case 
disease-producing 
bacteria  find  their 

FIG.  42. --The  contamination  of  water.  Way   into   the  drink- 

ing water.     Typhoid 

fever  and  other  diseases  are  often  spread  in  this  way.  Wells 
should  not  be  dug  or  drilled  close  to  cesspools,  for  water  from 
the  surrounding  soil  is  likely  to  drain  into  them.  Deep 
wells  are  less  likely  to  be  contaminated  than  shallow  ones, 
but  in  any  case  the  upper  part  of  the  veils  should  be  made 
water  tight  so  that  no  surface  water  can  enter.  The  water- 
tight casing  should  be  carried  down  to  a  layer  of  clay  or 
stone  through  which  the  surface  water  cannot  penetrate. 
A  spring  at  the  foot  of  a  hill  is  often  contaminated  from 
a  cesspool  on  the  hillside  above. 

15.  Boiled  Water  for  Drinking.  In  case  water  is  sus- 
pected of  contamination  the  only  safe  thing  to  do  is  to  boil 
it,  and  thereby  kill  the  bacteria.  Many  filtering  devices  are 
offered  for  sale,  but  no  small  household  filter  can  be  de- 
pended upon  to  remove  all  the  disease-producing  bacteria. 


WATER  37 

In  the  case  of  city  water  supply  large  filtering  beds  may  be 
constructed  which  will  purify  the  water,  but  even  these 
require  the  constant  care  of  the  expert  engineer  to  keep  them 
working  effectively.  Boiled  water  has  a  flat  taste  because 
of  the  fact  that  the  air  and  other  gases  have  been  driven 
out  by  the  boiling  process.  The  taste  of  such  water  may  be 
improved,  however,  by  beating  air  into  it  after  it  has  been 
thoroughly  cooled.  Rain  water,  or  cistern  water,  collected 
in  the  open  country,  may  be  used  for  drinking  purposes  with 
safety,  if  the  rain  is  first  allowed  to  wash  the  roof,  and  the 
cistern  is  carefully  protected  to  prevent  contamination. 

16.  Hard  Water.  Water  which  contains  a  large  amount 
of  mineral  matter  is  known  as  hard  water.  With  such 
waters,  soap,  instead  of  forming  suds,  produces  a  curd  which 
floats  on  top.  Hardness  is  for  the  most  part  caused  by  lime 
compounds  that  are  dissolved  in  the  water.  If  the  water 
is  boiled,  some  of  these  lime  compounds  are  made  insoluble 
and  separate,  leaving  the  water  less  hard  than  it  was.  Hard- 
ness which  can  be  removed  by  boiling  is  known  as  temporary 
hardness,  while  that  which  cannot  be  so  removed  is  called 
permanent  hardness.  These  terms  will  be  more  fully  ex- 
plained in  a  later  chapter.  Hard  water  is  unsuited  to  house- 
hold use  because  so  much  more  soap  is  required  with  it 
than  with  soft  water.  This  may  be  illustrated  by  a  sim- 
ple experiment.  Equal  quantities  (25  cc.)  of  distilled 
water,  rain  water,  fresh  well  water,  and  boiled  well  water 
are  placed  in  four  8-ounce  bottles.  A  one  per  cent  solu- 
tion of  a  pure  soap  (in  alcohol)  is  added  to  each  bottle, 
a  drop  at  a  time,  and  the  bottle  is  vigorously  shaken  after 
each  addition.  It  will  be  found  that  almost  the  first  drop 
will  make  suds  with  the  distilled  water ;  that  a  little  more 
will  be  required  with  the  rain  water;  and  that  the  well 


38 


INORGANIC  CHEMISTRY 


water  will  require  much  more  than  either  the  distilled  or 
the  rain  water.  The  boiled  well  water  will  produce  suds 
with  less  soap  than  the  fresh  well  water. 

Hard  water  is  not  satisfactory  for  use  in  boilers,  for  the 
mineral  matter  in  such  water  forms  a  crust  or  scale  on  the 
inside  of  the  boiler  much  like  that  found  on  the  inside  of  a 
teakettle  when  well  water  is  used.  In  limestone  countries, 
especially,  it  becomes  necessary  to  soften  the  water  before  it 
can  be  used  in  the  boilers.  This  is  done  by  the  addition  of 
boiler  compounds  made  of  various  chemicals  which  will 
throw  the  lime  or  calcium  salts  out  of  solution.  Borax, 
washing  soda,  quicklime,  sodium  phosphate,  and  other 
chemicals  are  used  for  this  purpose. 

17.  Mineral  Waters.  Mineral  waters  are  not  neces- 
sarily heavily  charged  with  mineral  matter,  but  usually 
contain  rather  large  amounts  of  one  substance  which  gives 
them  their  peculiar  characteristics.  Some  contain  mag- 
nesium compounds,  others  are  noted  for  the  iron  they  con- 
tain, and  still  others  are  so 
charged  with  carbon  dioxide  that 
they  effervesce  like  soda  water. 
Sulphur  water  and  lithia  waters 
are  also  found  in  nature. 

18.  Water  in  Organic  Matter. 
The  sources  of  water  heretofore 
mentioned,  such  as  wells,  rivers, 
and  lakes,  are  obvious;  but 
water  also  exists  under  conditions 

FIG.  43. -Showing  the  presence       not  SO  apparent.     It  is  Well  known 
of  water  in  organic  matter.  ^^  plants  and  animals  US6  large 

quantities  of  water  during  their  growth,  and  that  some  of 
the  water  remains  in  the  organism.  If  a  small  quantity 


WATER  39 

of  grass,  potato,  turnip,  corn,  or  a  bit  of  lean  meat  is  heated 
gently  in  a  test  tube,  as  shown  in  Fig.  43,  the  escaping  water 
will  be  condensed  in  droplets  at  the  top.  of  the  tube.  Vege- 
tables like  beets,  carrots,  turnips,  and  potatoes  are  90 
per  cent  water.  If  the  body  of  a  calf  weighing  150  pounds 
were  completely  dried,  it  would  be  found  to  weigh  only 
about  50  pounds.  In  other  words,  such  a  body  is  nearly 
two  thirds  water. 

19.  Water  of  Crystallization.     If  a  crystal  of  Glauber's 
salt  (sodium  sulphate)  is  heated  in  a  test  tube,  water  will  be 
driven  off  and  the  crystal  will  change  to  a  powder.     It  may 
be  inferred  from  this  experiment  that  the  crystal  contained 
water,  and  that  the  water  was  in  some  way  necessary  to  pro- 
duce the  crystalline  form.     If  a  crystal  of  blue  vitriol  (cop- 
per sulphate)  is  heated,  not  only  will  water  be  driven  off  and 
the  crystalline  form  be  destroyed,  but  the  blue  color  will 
disappear  as  well,  leaving  a  grayish  white  mass.     A  little 
water  added  to  this  mass  will  restore  the  blue  color,  and  if 
the  material  is  dissolved  in  a  small  quantity  of  hot  water 
and  allowed  to  stand,  blue  crystals  will  again  be  formed. 
Water  which  thus  forms  a  part  of  the  crystal  is  known  as 
water   of  crystallization.     Not   all   crystals   contain   water, 
however,  as  some  compounds  crystallize  without  water  of 
crystallization.     Quartz    and    potassium    dichromate    are 
examples  of  such  compounds. 

20.  Efflorescence  and  Deliquescence.     If  a  bright  crys- 
tal of  washing  soda  is  allowed  to  stand  exposed  to  the  air, 
it  gradually  gives  off  a  part  of  its  water  of  crystallization  and 
crumbles  to  a  white  powder.     Crystals  which  thus  give  off 
their  water  at  ordinary  temperatures  are  said  to  effloresce. 
Other  substances  have  such  a  strong  attraction  for  water 
that  they  will  take  it  from  the  air  until  they  actually  dis- 


40 


INORGANIC  CHEMISTRY 


solve  in  the  absorbed  water.  Such  materials  (of  which 
calcium  chloride  is  a  good  example)  are  said  to  deliquesce. 
Substances  which  rejnove  water  so  readily  from  the  air  will 
be  found  to  be  useful  in  drying  gases. 

21.  Water  May  Be  Decomposed.  Water  exists  in 
three  different  forms  —  solid,  liquid,  and  gaseous  water. 
These  differences,  however,  are  purely  physical.  Ice  may 
be  melted  to  water,  and  the  water  heated  to  steam  and  dis- 
tilled, and,  under  proper  conditions,  the  process  may  be 


FIG.  44.  — Apparatus  for  the  decomposition  of  water. 

reversed.  The  same  quantity  of  water  may  pass  through 
this  cycle  of  changes  an  indefinite  number  of  times,  but  it 
will  still  be  water.  If  the  steam  shown  in  Fig.  28  instead 
of  being  cooled  in  the  condenser  is  passed  over  certain  heated 
metals,  a  marked  change  takes  place,  as  can  be  easily  dem- 
onstrated by  the  following  experiment : 

A  small  quantity  of  powdered  zinc  is  placed  in  the  hard 
glass  tube  B  in  Fig.  44.  The  flask  A  is  one  third  full  of 
water  and  the  bottle  C  is  filled  with  water  and  inverted  in 
the  dish  D.  The  water  in  A  is  boiled  until  the  steam  has 


WATER  41 

driven  all  the  air  out  of  the  apparatus,  and  then  the  burners 
are  lighted  under  the  hard  glass  tubing  B.  When  the  zinc 
becomes  hot  the  end  of  the  rubber  tubing  E  is  slipped  under 
the  mouth  of  the  bottle  C.  Bubbles  of  gas  will  soon  enter 
the  bottle.  When  the  bottle  is  filled  with  the  gas,  the  rubber 
tubing  is  withdrawn  and  the  flames  are  extinguished. 

The  gas  in  the  bottle  is  colorless  and  as  far  as  outward 
appearance  goes  might  be  air.  It  cannot  be  steam ;  for  if  it 
were,  it  would  be  cooled  by  the  water  and  condensed.  If 
the  bottle  is  carefully  lifted  mouth  down  and  a  lighted  splint 
or  candle  is  introduced,  the  gas  will  ignite  and  burn  with  a  pale 
blue  flame.  Clearly  here  is  a  gas  which  has  been  obtained 
from  the  water  but  which  has  none  of  the  characteristics  of 
water.  The  heated  zinc  has  decomposed  the  water,  and  this 
gas  is  one  of  the  resulting  products.  This  gas  was  first  dis- 
covered by  the  English  investigator  Cavendish  in  1766.  It 
was  named  hydrogen  by  the  French  chemist,  Lavoisier,  be- 
cause it  is  one  of  the  constituents  of  water. 

EXERCISES 

Ex.  12.  Add  one  gram  of  salt  to  a  test  tube  of  water.  Do  the  same 
with  pure  sand.  What  difference  do  you  notice?  Are  all  substances 
soluble?  Try  a  little  gypsum  (calcium  sulphate).  Can  you  prove 
that  any  of  it  dissolves  ?  Are  all  soluble  substances  equal  in  solubility  ? 

Ex.  13.  Add  1  cc.  of  alcohol  to  10  cc.  of  water.  Do  the  same 
with  coal  oil.  What  difference  do  you  notice?  What  is  meant  by 
the  statement  that  a  liquid  is  miscible  with  water  ? 

Ex.  14.  Heat  some  well  water  or  tap  water  in  a  beaker.  What 
are  the  bubbles  that  appear  ?  Are  gases  soluble  in  water  ?  How  does 
pressure  affect  the  solubility  of  gases  in  water?  How  does  rise  of 
temperature  affect  the  solubility  of  gases  ?  Of  solids  ? 

Ex.  15.  Dissolve  ten  grams  of  salt  in  100  cc.  of  water  in  a  flask 
and  heat  the  solution  to  boiling.  Determine  the  temperature  of  the 
solution.  How  does  the  dissolved  salt  affect  the  boiling  point  ?  Wipe 


42  INORGANIC  CHEMISTRY 

off  the  thermometer  and  test  the  temperature  of  the  steam  above  the 
water.  What  is  the  temperature?  To  fix  the  100°  point  in  a  ther- 
mometer, would  it  be  best  to  put  the  bulb  in  the  boiling  water  or  in 
the  steam?  If  salt  were  placed  in  the  water  in  the  outer  pan  of  a 
double  boiler,  what  effect  would  it  have  on -the  temperature  of  the 
material  being  cooked  in  the  inner  pan  ? 

Ex.  16.  Mix  one  gram  of  bicarbonate  of  soda  with  a  like  amount 
of  dry  powdered  tartaric  acid.  Do  you  notice  any  change?  Add  a 
few  drops  of  water.  What  change  do  you  notice  now?  What  effect 
does  water  have  on  chemical  action? 

Ex.  17.  What  is  meant  by  a  potable  water  ?  Is  the  mineral  matter 
in  well  water  ordinarily  injurious  ?  What  is  the  chief  source  of  danger 
in  drinking  water  ?  Why  should  wells  never  be  near  cesspools  ?  Which 
are  safer,  deep  or  shallow  wells?  How  should  wells  be  protected  at 
the  surface?  How  can  contaminated  water  be  made  safe  to  drink? 
Is  cistern  water  ever  fit  for  drinking  ? 

Draw  a  plan,  where  well  or  spring  water  is  used,  showing  the 
location  of  your  water  supply  and  its  distance  from  cesspools,  manure 
piles,  or  other  possible  sources  of  sewage  contamination.  Observe 
also  whether  the  natural  drainage  slope  from  such  sources  of  con- 
tamination is  towards  or  away  from  the  water  supply.  Do  you  find 
that  a  safe  or  an  unsafe  condition  exists?  Can  unsatisfactory  condi- 
tions be  improved  by  change  in  location,  or  in  a  modification  of  the 
direction  of  drainage?  Draft  a  plan  which  if  applied  would  be  an 
improvement  on  the  present  arrangement.  What  is  the  only  safe 
course  to  pursue  with  reference  to  drinking  water  when  changes  in 
present  conditions  cannot  be  made  ? 

Ex.  18.  Make  fine  shavings  of  Castile  soap  and  dissolve  .5  gram  in 
50  cc.  of  alcohol.  Place  25  cc.  of  rain  water  in  an  8-oz.  bottle.  By 
means  of  a  medicine  dropper  add  the  soap  solution,  one  drop  at  a 
time,  to  the  water  and  shake  vigorously  after  each  addition.  Continue 
until  a  suds  is  formed  which  will  stand  for  at  least  a  minute.  Record 
the  number  of  drops  of  soap  solution  used.  Repeat  the  experiment 
with  distilled  water,  well  water,  and  boiled  well  water.  Which  water 
required  the  most  soap?  Which  the  least?  Why  is  rain  water  pre- 
ferred to  well  water  in  the  laundry  ?  Was  there  any  difference  between 
the  boiled  and  the  unboiled  well  water  ?  What  is  meant  by  hardness  of 
water?  By  temporary  hardness?  By  permanent  hardness?  Ex- 


WATER 


43 


amine  the  inside  of  the  teakettle  at  home.  Is  there  any  mineral 
matter  on  the  inside  of  the  kettle  ?  How  do  you  account  for  it  ?  Would 
you  expect  more  scale  in  the  kettle  in  a  sandstone  country  or  in  a  lime- 
stone country  ?  What  are  mineral  waters  ? 

Ex.  19.  Heat  small  quantities  of  grass,  potato,  or  other  vegetables 
in  a  test  tube  (Fig.  43).  What  do  you  notice?  Repeat  the  experi- 
ment with  a  bit  of  lean  meat.  What  can  you  say  about  water  in 
organic  matter? 

Ex.  20.  Select  a  clear  crystal  of  sodium  sulphate  and  heat  in  a  test 
tube.  Does  water  come  off?  What  is  this  water  called?  What  has 
happened  to  the  crystal  ?  Repeat  the  experiment  with  a  crystal  of  cop- 
per sulphate.  What  happens  to  this  crystal  ?  Has  the  color  changed  ? 
Add  a  few  drops  of  water.  What  happens  to  the  color  ?  Dissolve  in  a 


FIG.  45.  —  A  simple  apparatus  for  decomposing  water  by  means  of  zinc  dust. 

small  quantity  of  hot  water  and  set  aside  to  crystallize.  Do  the  crystals 
resemble  the  one  you  started  with  ?  Is  water  necessary  to  all  crystals  ? 
Heat  a  crystal  of  potassium  bichromate.  What  do  you  observe  in  this 
case? 

Ex.  21.  Select  a  bright  crystal  of  washing  soda  and  allow  it  to 
stand  exposed  to  the  air  for  several  hours.  What  happens  to  the 
crystal?  What  term  is  used  for  such  substances?  Try  the  same 
experiment  with  calcium  chloride.  What  do  you  observe  in  this  case  ? 
What  term  is  used  for  such  substances? 


44  INORGANIC  CHEMISTRY 

Ex.  22.  Arrange  apparatus  as  in  Fig.  44.  The  tube  B  may  be  of 
hard  glass  or  it  may  be  a  piece  of  one-half-inch  iron  gas  pipe.  Place 
powdered  zinc  in  the  tube.  Boil  the  water  in  the  flask  A  so  that 
steam  will  pass  over  the  zinc,  which  is  heated  to  low  redness  by  the 
burner  beneath.  The  air  is  first  driven  out,  and  then  pure  steam 
passes  over.  Finally  when  the  zinc  becomes  hot  gas  begins  to  ap- 
pear. Collect  one  or  two  bottles  of  gas  in  the  manner  described  in 
Section  21.  What  is  the  appearance  of  the  gas?  Carefully  lift  the 
bottle  and  apply  a  lighted  splint  to  the  mouth.  What  happens? 
What  is  the  name  of  this  gas  ?  Who  first  discovered  it  ? 

Note.  This  experiment  may  be  conducted  in  the  apparatus  shown 
in  Fig.  45.  A  is  a  hard  glass  test  tube.  Zinc  dust  is  placed  at  B. 
The  steam  from  C  is  decomposed  in  the  same  way  as  in  Ex.  22.  This 
experiment  is  made  more  striking  if  magnesium  tape  is  used  in  the 
place  of  the  zinc,  as  the  magnesium  can  be  seen  to  burn  in  the  steam. 
A  piece  of  magnesium  tape  one  foot  long  will  furnish  sufficient  gas 
to  fill  an  8-oz.  bottle. 


CHAPTER  III 
HYDROGEN 

22.  Preparation.  Hydrogen  may  be  prepared  by  passing 
steam  over  heated  zinc,  iron,  or  other  metals  in  the  manner 
described  in  the  preceding  chapter,  but  these  methods  are 
not  convenient  when  the  gas  is  required  in  large  quantities. 
The  preparation  of  hydrogen  in  the  laboratory  is  usually 

a 


FIG.  46.  —  Apparatus  for  the  preparation  of  hydrogen. 

accomplished  by  the  action  of  sulphuric  acid  on  zinc  or  iron. 
Zinc  is  ordinarily  employed  because  most  samples  of  iron 
contain  impurities  which  contaminate  the  hydrogen.  In  the 
wide-mouth  bottle  A  (Fig.  46)  there  is  placed  a  small  quan- 
tity of  granulated  zinc,  and  water  is  poured  into  the  thistle 
tube  B  until  the  zinc  is  covered.  The  end  of  the  thistle 
tube  must  be  beneath  the  water.  Dilute  sulphuric  acid 
is  then  poured  down  the  thistle  tube.  An  active  evolution 

45 


46 


INORGANIC  CHEMISTRY 


of  gas  takes  place,  and  when  sufficient  time  has  elapsed 
for  the  hydrogen  to  drive  all  the  air  out  of  the  apparatus, 
the  gas  is  collected  over  water  in  the  wide-mouth  bottle  D. 
The  hydrogen  in  this  case  is  contained  in  the  sulphuric  acid 
and  is  replaced  or  driven  out  by  the  zinc. 

23.  Properties.      Hydrogen  is  a  gas  that  has  no  taste, 
color,  or  odor.     It  will  burn  readily,  and  when  it  is  mixed 
with  air  the  combustion  takes  place  with  an  explosion.     Hy- 
drogen is  the  lightest  known  substance  and  weighs  less  than 

one  fourteenth  as  much 
as  air.  For  this  reason 
it  was  used  formerly  to 
fill  balloons;  but  it  is 
now  largely  superseded 
by  ordinary  illuminating 
gas,  which  is  less  expen- 
sive. It  is  still  used  for 
the  airship  or  dirigible 
balloon.  That  hydro- 
gen is  lighter  than  air  is  shown  by  the  fact  that  it  can 
be  poured  upwards.  A  bottle  full  of  hydrogen  is  gradually 
turned  mouth  upward  beneath  an  inverted  bottle  filled  with 
air  (Fig.  47).  If  after  a  minute  or  two  a  lighted  splint  is 
applied  to  the  mouths  of  the  two  bottles,  it  will  be  found 
that  the  hydrogen  has  passed  out  of  the  bottle  A  into  B. 
The  same  thing  is  shown  by  blowing  soap  bubbles  with  hydro- 
gen ;  in  which  case,  owing  to  the  lightness  of  the  gas,  the 
bubbles  will  rise  rapidly  in  the  air. 

24.  When   Hydrogen  Burns   Water    is  Formed.      The 
apparatus  shown  below  may  be  used  to  study  the  behavior 
of  hydrogen  when  burning  quietly  in  the  air  (Fig.  48). 

The  bottle  A  is  the  hydrogen  generator  already  described. 


FIG.  47.  —  Pouring  hydrogen  upwards. 


HYDROGEN 


47 


B  is  a  tube  containing  calcium  chloride  to  dry  the  hydrogen. 
After  the  gas  has  been  carefully  tested  to  make  sure  that  all 
air  has  been  driven  out  of  the  apparatus,  the  jet  is  ignited 


FIG.  48.  — Apparatus  for  showing  behavior  of  hydrogen  when  burning  in  the  air. 

at  C.  The  flame  will  be  found  to  be  intensely  hot.  Pure 
hydrogen  burns  with  a  pale  blue  flame,  but  in  such  an  appa- 
ratus it  is  likely  to  be  colored  yellow  by  the  sodium  in  the 
glass.  If  a  bell  jar  or  a  large  bottle  is  held  in  the  position 
shown  by  D,  moisture  will  collect  on  the  interior  until  it 
runs  down  the  sides  as  indicated.  When  hydrogen  is  burned, 
water  is  always  produced. 

25.  Occurrence.  Hydrogen  is  not  found  in  nature  in 
the  free  state  except  in  the  merest  traces.  It  is,  however, 
very  abundant  and  very  widely  distributed  in  combination 
with  other  substances.  It  is  found  in  water  as  has  been 
shown,  and  it  is  also  a  part  of  nearly  all  animal  and  vege- 
table substances.  Crude  petroleum  and  all  the  products 
made  therefrom  contain  hydrogen.  When  any  substance 
containing  hydrogen  is  burned  in  air,  water  is  formed,  as  can 


48  INORGANIC  CHEMISTRY 

be  shown  by  holding  a  cold  bottle  or  piece  of  glass  over  the 
flame  of  a  candle,  kerosene  lamp,  or  gas  jet.  Candles,  kero- 
sene, and  gas  all  contain  hydrogen,  and  a  film  of  moisture 
will  be  deposited  on  any  cold  surface  held  above  the  flame. 

26.  Water  Contains  Something  Besides  Hydrogen.     In 
the  experiment  described  in  section  21,  it  was  shown  that 
hydrogen  could  be  prepared  from  water.     This  gas  is  so 
different  from  water,   however,   that  water  must  contain 
something  in  addition  to   hydrogen ;  or,   in   other  words, 
hydrogen  is  combined  with  something  else  to  form  water. 
An  examination  of  the  zinc  in  the  hard  glass  tube  will  show 
that  part  of  it  has  changed  in  appearance,  an  occurrence 
which  indicates  that  something  from  the  water  has  combined 
with  the  zinc.     It  will  be  interesting  to  try  to  ascertain 
what  the  other  substance  or  substances  in  water  may  be. 

27.  Electrolysis  of  Water.     Water  and  many  other  sub- 
stances can  be  decomposed  by  the  electric  current.     The 
effect  of    the    electric    current    on  water    can  be    readily 
shown  in  the  apparatus  illustrated  in  Fig.  49.     Platinum 
wires,  to  the  ends  of  which  are  attached  pieces  of  platinum 
foil,  are  fused  into  the  tubes  B  and   C.      The   stopcocks 
at  the  top  of  the  tubes  are  opened,  and  the  apparatus  is 
filled  with  water  containing  about  one  tenth  of  its  volume 
of  sulphuric  acid.     The  water  is  put  into  the  apparatus  at 
A.    The  sulphuric  acid  is  used  because  pure  water  will  not 
conduct  electricity.      The  stopcocks  are   now   closed,  and 
the  platinum  wires  in  the  tubes  B  and  C  are  connected  with 
wires  leading  to  a  battery.     Three  or  more  dry  cells,  or  two 
or  three  dichromate  cells,  will  serve  the  purpose.     As  soon 
as  the  current  begins  to  pass  through  the  water,  bubbles  of 
gas  will  be  noticed  passing  from  the  platinum  foil  to  the 
upper  part  of  the  tube.     It  will  be  seen  that  more  gas  col- 


HYDROGEN 


49 


lects  in  one  tube  than  in  the  other,  and  it  will  soon  be  appar- 
ent that  one  tube  contains  exactly  twice  as  much  gas  as 
the  other.  Both  of  the  gases  must  have  come  from  water, 
for  a  careful  analysis  would  show  that  all  the  sulphuric  acid 
added  still  remains  in  the 
apparatus. 

The  larger  volume  is  on 
the  side  connected  with  the 
negative  pole  of  the  battery. 
When  this  tube  is  nearly  full 
of  the  gas,  the  battery  is  dis- 
connected and  the  gases  are 
examined.  By  attaching  a 
small  rubber  tube  to  the  tip 
of  the  stopcock  the  gases 
may  be  collected  in  test 
tubes  over  water  in  the  usual 
way.  The  gas  from  the  side 
containing  the  double  vol- 
ume burns  in  such  a  way  as 
to  show  that  it  is  hydrogen, 
but  the  other  gas  behaves 
quite  differently.  It  does 
not  burn,  but  if  a  splint  with 
a  glowing  coal  on  the  end  is 
thrust  into  the  test  tube 
containing  this  gas,  it  will  burst  into  a  flame.  Here,  then,  is 
a  new  gas  which  does  not  burn,  but  which  causes  the  splint 
to  burn  more  vigorously  than  it  did  in  the  air. 

This  gas  was  discovered  at  about  the  same  time  (1774-75) 
by  the  English  chemist  Priestley  and  the  Swedish  chemist 
Scheele,  although  each  was  working  independently.  Lavoi- 

EV.    CHEM. 4 


FIG.  49.  —  Method  of  decomposing 
water  by  the  electric  current. 


50  INORGANIC  CHEMISTRY 

sier,  the  French  chemist,  gave  it  the  name  oxygen  (meaning 
acid-former),  because  he  thought  that  all  acids  owed  their 
properties  to  this  substance,  a  view  now  known  to  be  incor- 
rect. 

EXERCISES 

Ex.  23.  Arrange  apparatus  as  in  Fig.  46.  A  is  an  8-oz.  wide-mouth 
bottle.  Place  10  grams  of  granulated  zinc  in  this  bottle  and  add  suffi- 
cient water  to  cover  the  zinc  and  the  end  of  the  thistle  tube.  Prepare 
dilute  sulphuric  acid  by  slowly  pouring  15  cc.  of  the  strong  acid  into 
50  cc.  of  water,  stirring  constantly.  Never  pour  the  water  into  the 
acid.  Now  pour  a  little  of  the  dilute  acid  down  the  thistle  tube. 

(Note.  Chemically  pure  zinc  and  sulphuric  acid  will  not  react. 
It  is  advisable,  therefore,  to  add  a  few  drops  of  a  solution  of  copper 
sulphate  to  the  water  in  the  bottle  A.) 

Acid  is  added  from  time  to  time  to  keep  up  a  steady  flow  of  gas. 
After  the  air  has  all  been  driven  out  of  the  apparatus  collect  four 
bottles  of  the  gas.  What  was  the  source  of  the  hydrogen?  Describe 
the  appearance  of  the  gas. 

Ex.  24.  Hold  a  bottle  of  the  gas  mouth  downward  and  apply  a 
lighted  splint.  Describe  the  result.  What  does  this  prove  about  the 
gas? 

Ex.  25.  Fill  a  2-oz.  wide-mouth  bottle  half  full  of  water,  invert  in 
the  pan  of  water,  and  fill  with  hydrogen.  What  does  the  bottle  con- 
tain? Hold  it  at  arm's  length,  mouth  downward,  and  ignite  over  a 
candle  or  burner.  What  happens  ?  What  does  this  prove  ? 

Ex.  26.  Gradually  turn  a  bottle  of  hydrogen  mouth  upward  under 
a  similar  bottle  filled  with  air  (Fig.  47).  After  a  minute  apply  a 
lighted  splint  to  both  bottles.  Describe  the  results.  Is  hydrogen 
lighter  or  heavier  than  air  ? 

Ex.  27.  Arrange  apparatus  as  in  Fig.  48.  Add  the  dilute  sul- 
phuric acid,  and  when  hydrogen  has  been  evolved  for  some  minutes 
test  the  purity  of  the  gas  by  collecting  test  tubes  of  the  gas  and  igniting 
them,  mouth  downward.  If  all  air  is  out  of  the  apparatus,  the  hydrogen 
will  burn  quietly ;  otherwise  it  will  explode.  When  you  are  sure  that 
only  pure  hydrogen  is  coming  off,  wrap  a  towel  around  the  bottle  and 


HYDROGEN  51 

ignite  at  C.  Test  the  heat  of  the  flame  by  holding  a  piece  of  iron  in 
it.  Hold  a  large  wide-mouth  bottle  or  bell  jar  over  the  flame.  What 
is  the  result  ?  What  is  formed  when  hydrogen  burns  ? 

Ex.  28.  Hold  a  wide-mouth  bottle  or  a  bell  jar  over  the  flame  of  a 
candle,  an  alcohol  lamp,  or  a  gas 'burner,  at  home.  Does  moisture 
collect  on  the  side  of  the  bottle  ?  What  is  the  source  of  the  moisture  ? 

Ex.  29.  Fill  the  apparatus  shown  in  Fig.  49  with  water  containing 
one  tenth  its  volume  of  sulphuric  acid.  Connect  the  platinum  wires 
with  a  battery  (four  dry  cells  will  do)  and  watch  the  gas  collect  in  the 
two  arms  of  the  apparatus.  Which  side  contains  the  most  gas  ?  With 
which  pole  of  the  battery  is  it  connected  ?  What  is  the  source  of  these 
two  gases?  When  the  tube  containing  the  larger  quantity  of  gas  is 
nearly  full,  disconnect  the  battery.  Place  a  piece  of  small  rubber 
tubing  over  the  tip  of  the  stopcock  on  the  tube  containing  the  double 
quantity  of  gas  and  collect  the  gas  in  a  test  tube  over  water.  Test  it 
with  a  flame.  What  is  this  gas?  Collect  the  gas  from  the  other  side 
in  the  same  way.  Test  it  by  holding  the  test  tube  mouth  upward 
and  thrusting  into  it  a  splint  with  a  glowing  coal  on  the  end.  What 
happens  in  this  case?  Does  this  gas  behave  like  hydrogen?  What 
name  has  been  given  to  this  gas?  Who  discovered  it?  By  whom 
was  it  named? 


CHAPTER  IV 
OXYGEN 

28.  Preparation.  Oxygen  may  be  prepared  from  water 
by  electrolysis,  as  described  in  the  last  chapter,  but  it  is 
more  commonly  prepared  in  the  laboratory  by  heating  some 
substance  which  contains  it.  The  material  generally  used 


FIG.  50.  —  Preparing  oxygen  from  potassium  chlorate  and  manganese  dioxide. 

is  the  white  salt  known  as  potassium  chlorate  (often  called 
chlorate  of  potash).  This  substance  contains  thiriy-nine 
per  cent  of  oxygen,  which  may  be  driven  off  at  high  tempera- 
ture. For  some  unknown  reason,  however,  the  oxygen  is 
liberated  at  a  much  lower  temperature  if  the  potassium 
chlorate  is  mixed  with  about  one  fourth  its  own  weight  of 
the  black  substance  known  as  manganese  dioxide.  The 
manner  of  preparing  oxygen  is  illustrated  in  Fig.  50. 

52 


OXYGEN 


53 


FIG.  51.  —  Copper 
flask  for  making 
oxygen. 


The  mixture  of  potassium  chlorate  and  manganese  dioxide 
is  placed  in  the  flask  A,  which  stands  on  a  small  sandbath. 
When  this  is  gently  heated,  the  gas  soon 
begins  to  pass  through  the  tube  B  and  is 
collected  over  water  in  the  bottles  C.  The 
gas  is  not  collected  until  the  air  has  all 
been  driven  out  of  the  apparatus.  Be- 
fore the  burner  is  removed  (at  the  end 
of  the  experiment)  the  rubber  tube  B  is 
disconnected  to  prevent  the  water  from 
being  drawn  back  into  the  flask  as  it  cools.  When  large 
quantities  of  oxygen  are  to  be  prepared,  the  copper  flask, 
shown  in  Fig.  51,  is  used  instead  of  a  glass  flask,  which  is 
easily  broken. 

29.  Properties.  Oxygen  is  a  colorless,  odorless,  and 
tasteless  gas,  which  is  1.1  times  heavier  than  air.  Its  most 
interesting  property  is  the  way  in  which  it  supports  combus- 
tion. Materials  which  burn  in  the  air  burn  much  more 
rapidly  in  oxygen.  If  a  splint  with  a  glowing  coal  on  the 
end  is  thrust  into  a  bottle  of  oxygen,  it  .will 
burst  into  flame  and  burn  vigorously.  Sul- 
phur burns  with  a  feeble  flame  in  the  air, 
but  in  oxygen  the  flame  is  increased  in  size 
and  brightness.  Phosphorus  burns  readily 
in  the  air,  but  in  oxygen  it  burns  with  a 
dazzling  brilliance.  Some  substances  that 
will  not  burn  in  the  air  will  do  so  in  pure 
oxygen.  Take  a  piece  of  picture  frame  wire, 
heat  the  end  in  a  Bunsen  burner,  and  dip 
into  powdered  sulphur.  The  sulphur  will 
adhere  to  the  end  of  the  wire,  and  if  it  is  ignited  in  the 
burner  and  then  thrust  into  a  jar  of  oxygen,  the  wire  will 


FIG.  52.  —Burn- 
ing iron  wire  in 
oxygen. 


54  INORGANIC  CHEMISTRY 

burn  with  brilliant  scintillation  (Fig.  52).  Glowing  balls  of 
molten  matter  drop  from  the  wire  to  the  bottom  of  the  jar. 
Hydrogen  mixed  with  half  its  volume  of  oxygen  explodes 
when  ignited  much  more  violently  than  it  does  when  mixed 
with  air.  Experiments  with  mixtures  of  these  two  gases 


H 


v    SECT/O/V  ro  SHOW  co/vsr/evcr/OH 
FIG.  53.  —  Oxy-hydrogen  blowpipe. 

should  be  conducted  with  great  caution.  The  flame  made 
by  burning  hydrogen  in  oxygen  is,  with  one  exception,  the 
hottest  known.  To  make  use  of  this  flame  a  special  oxy- 
hydrogen  burner  is  used  which  permits  the  gases  to  mix 
only  at  the  nozzle  (Fig.  53).  When  this  flame  plays 
against  a  piece  of  lime,  it  heats  it  to  a  white  heat  and  forms 
the  so-called  "  limelight,"  sometimes  used  for  stereopt icons. 

30.  Composition  of  Water.  The  decomposition  of  water 
by  electrolysis  shows  that  both  hydrogen  and  oxygen  are 
contained  in  water,  but  this  experiment  alone  does  not  prove 
that  water  is  composed  solely  of  hydrogen  and  oxygen.  If 
these  two  substances  can  be  combined  to  form  water,  the 
proof  that  water  is  composed  only  of  these  two  substances 
will  be  conclusive.  This  has  frequently  been  done  by  means 
of  the  apparatus  shown  in  Fig.  54. 

A  is  a  graduated  tube,  known  as  a  eudiometer,  which  has 
two  platinum  wires  fused  into  the  closed  end,  the  ends  of 
the  wires  being  about  2  mm.  apart.  This  tube  is  filled  with 
mercury  and  inverted  in  a  cylinder  B  full  of  mercury.  Hy- 
drogen gas  is  then  introduced  into  the  tube  A,  and  the  vol- 


OXYGEN  55 

ume  is  carefully  determined  by  raising  or  lowering  the  eu- 
diometer until  the  mercury  is  at  the  same  level  inside  and 
outside  of  the  tube.  It  is  an  easy  matter  to  determine  the 
volume  since  it  may  be  read  on  the  scale.  Oxygen  gas  is  then 
introduced  and  measured  in  the  same  way. 
Nothing  occurs  to  the  mixture  of  gases  if 
allowed  to  stand  at  ordinary  temperatures; 
but  if  an  electric  spark  is  caused  to  pass  be- 
tween the  two  platinum  wires,  the  gases  will 
unite  with  a  slight  explosion.  If  the  gases 
are  mixed  in  the  proportion  of  exactly  two 
volumes' of  hydrogen  to  one  of  oxygen,  they  will 
disappear  entirely,  and  nothing  will  be  left 
but  a  minute  quantity  of  water.  That  the 
quantity  of  water  is  so  small  is  due  to  the 
fact  that  the  combined  volumes  of  the  hydro-  ' 
gen  and  oxygen  required  to  produce  water  is 
over  2500  times  the  volume  of  the  resulting  FIG.  54.  —  Eudi- 
water.  For  example,  if  one  cubic  centimeter 
of  water  were  decomposed  into  hydrogen  and  oxygen,  the 
combined  gases  would  have  a  volume  of  over  2500  cubic 
centimeters. 

31.  Proportion  of  Hydrogen  and  Oxygen  in  Water.  If 
the  hydrogen  in  the  eudiometer  is  more  than  twice  the 
volume  of  the  oxygen,  an  excess*  of  hydrogen  will  remain 
after  the  explosion.  On  the  other  hand  if  the  oxygen  is 
more  than  half  the  volume  of  the  hydrogen,  an  excess  of 
oxygen  will  remain  uncombined.  Repeated  experiments 
of  this  kind  have  demonstrated  that  water  is  composed  of 
hydrogen  and  oxygen,  and  that  these  gases  always  combine 
in  the  ratio  of  one  volume  of  oxygen  to  two  of  hydrogen. 
As  the  weight  of  a  given  volume  of  oxygen  is  sixteen  times 


56  INORGANIC  CHEMISTRY 

that  of  the  same  volume  of  hydrogen,  it  follows  that  water 
is  composed  of  one  part  by  weight  of  hydrogen  to  eight  parts 
by  weight  of  oxygen. 

32.  Analysis    and   Synthesis.      Two   different   methods 
have  been  suggested  for  determining  the  composition  of 
water.     In  the  last  chapter  the  method  described  was  the 
decomposition  of  water  by  means  of  the  electric  current. 
A  process  in  which  a  substance  is  separated  into  its  component 
parts  is  termed  analysis.    The  decomposition  of  water  by 
means  of  heated  zinc  resulting  in  the  formation  of  hydrogen 
is  also  a  method  of  analysis.     Such  a  process  as  the  formation 
of  water  in  the  eudiometer,  in  which  a  substance  is  formed 
by  bringing  about  the  combination  of  its  component  parts, 
is  termed  synthesis. 

33.  Elements  and  Compounds.     It  has  been  shown  that 
water,  which  appears  to  be  a  simple  substance,  is  in  reality 
composed  of  two  substances  —  hydrogen   and   oxygen.     It 
is  natural  to  think  that  if  water  can  be  decomposed  into  two 
substances  it  might  be  possible  to  decompose  hydrogen  and 
oxygen.     All  attempts  to  get  anything  else  out  of  these  sub- 
stances, however,  have  failed.     In  other  words,  hydrogen 
and  oxygen  are  such  simple  substances  that  so  far  as  is  now 
known  they  cannot  possibly  be  divided  any  further.     Such 
substances  which  cannot  be  split  up  into  anything  simpler 
are  called  elements. 

Water,  which  is  a  union  of  hydrogen  and  oxygen,  is  a 
representative  of  that  class  of  substances  which  are  composed 
of  two  or  more  elements  united.  Substances  that  are  com- 
posed of  two  or  more  elements  are  called  compounds.  Water, 
therefore,  is  a  compound. 

The  study  of  chemistry  has  shown  that  the  number  of 
elements  is  quite  small,  only  about  eighty  in  fact.  Of  the 


OXYGEN  57 

known  elements,  not  more  than  twenty  are  of  everyday  im- 
portance. These,  only,  will  be  studied  in  this  text.  A 
complete  list  of  the  elements  is  given  on  the  inside  of  the 
back  cover. 

Although  the  number  of  elements  is  small,  many  thou- 
sands of  compounds  are  known,  and  the  list  is  being  con- 
tinually increased.  Water,  sugar,  salt,  alcohol,  ammonia, 
and  starch  are  familiar  compounds.  Oxygen,  iron,  lead, 
sulphur,  and  carbon  are  well-known  elements. 

34.  Definite    Proportions.       It    has    been    shown    (31) 
that  water  is  composed  of  eight  parts  by  weight  of  oxygen 
to  one  part  by  weight  of  hydrogen.     This  proportion  never 
varies  no  matter  whether  the  water  be  obtained  by  melting 
pure  ice,  by  condensing  steam,  or  by  burning  hydrogen. 
Careful  analysis  of  many  chemical  compounds  has  demon- 
strated that  this  is  a  general  rule,  and  that  a  chemical  com- 
pound always  contains  the  same  elements,  and  that  these 
elements  are  always  present  in  exactly  the  same  proportions 
by  weight.    This  fact  is  known  as  the  law  of  definite  propor- 
tions. 

35.  Physical   and   Chemical   Changes.      Two   different 
kinds  of  changes  in  water  have  also  been  observed.     Ice 
can  be  changed  to  water  and  water  to  steam ;   and  the  pro- 
cess may  be  reversed.     But  whether  it  exists  as  a  solid, 
liquid,  or  vapor,  it  is  still  water.     Such  a  change,  which 
merely  affects  the  form  and  does  not  affect  the  composition 
of  the  substance,  is  known  as  a  physical  change.     When 
water  is  decomposed  into  hydrogen  and  oxygen,  or  when 
these  two  gases  are  united  by  the  heat  of  the  electric  spark, 
the  change  which  takes  place  is  quite  different ;  for  in  either 
case  the  products  of  the  change  are  entirely  different  from 
the  substance  or  substances  undergoing  the  change.     Such 


58 


INORGANIC  CHEMISTRY 


a  change  as  this,  which  affects  the  composition  of  the  sub- 
stance, is  called  a  chemical  change. 

Two  other  terms  may  be  explained  here ;  namely,  mechani- 
cal mixture  and  chemical  compound.  In  a  mechanical  mix- 
ture the  substances  do  not  undergo  a  chemical  change, 
but  each  retains  all  of  its  individual  characteristics.  The 
mere  mixing  of  the  gases  hydrogen  and  oxygen  in  the  eudi- 
ometer is  a  good  example.  In  the  case  of  a  chemical  com- 
pound two  or  more  elements  have  undergone  a  chemical 
change,  and  have  united  and  thus  lost  their  original  char- 
acteristics. Water,  which  is  formed  by  the  chemical  union 
of  hydrogen  and  oxygen,  is  a  good  example  of  a  chemical 
compound. 

Physical  changes  and  mechanical  mixtures  may  be  said  to 
be  in  the  realm  of  physics,  while  the  chemical  changes  are  in 
the  field  of  chemistry. 

EXERCISES 

Ex.  30.     Arrange  apparatus  as  shown  in  Fig.  55. 
A  is  a  hard  glass  test  tube,  B  a  piece  of  glass  tubing 
bent  at  a  right  angle,  C  a  piece  of  rubber  tubing.    Make 
a  mixture  of   5   grams   of  potassium 
chlorate  and  half  its  bulk  of  manganese 
dioxide  by  rubbing  the  two  together 
in  a  mortar.     (As  manganese  dioxide 
sometimes    contains     impurities,    the 
mixture  should  be  tested  before  using 


FIG.  55,  —  A  simple  apparatus  for  generating  oxygen. 


OXYGEN  50 

by  heating  about  one  gram  in  a  test  tube.  If  the  oxygen  comes  off 
quietly,  proceed  with  the  experiment.)  Place  the  mixture  in  the  test 
tube  and  heat  gradually,  beginning  at  the  top.  A  steady  flow  of  gas 
may  be  obtained  by  regulating  the  amount  of  heat  applied.  Collect 
four  8-ounce  bottles  of  the  gas  in  the  usual  way.  At  the  end  of  the 
experiment  withdraw  the  tubing  from  the  water,  or  remove  the  cork 
from  the  test  tube.  What  is  the  appearance  of  the  gas  ?  (The  cloudi- 
ness which  sometimes  shows  at  the  beginning  of  the  experiment  will 
soon  disappear.) 

Ex.  31.  (a)  Slip  a  glass  plate  over  the  mouth  of  one  of  the  bottles 
and  turn  it  mouth  upward.  Thrust  a  splint  with  a  glowing  coal  on 
the  end  into  the  bottle  repeatedly. 

(6)  Warm  a  glass  rod  so  that  a  piece  of  sulphur  (the  size  of  a  grain 
of  wheat)  will  adhere  to  it.  Ignite  the  sulphur  and  note  how  it  burns. 
Thrust  it  into  a  bottle  of  oxygen  and  note  whether  it  burns  differently. 

(c)  Take  a  piece  of  picture  frame  wire  8  inches  long  and  spread  one 
end  slightly.  Heat  this  end  of  the  wire  and  dip  it  into  powdered  sulphur. 
Ignite  the  sulphur  which  adheres  to  the  wire  and  thrust  it  into  a  bottle 
of  oxygen.  What  happens  to  the  glowing  coal?  Does  the  oxygen 
ignite  as  hydrogen  did?  What  difference  do  you 
note  in  the  sulphur  burning  in  air  and  oxygen?  Is 
the  odor  the  same  in  each  case  ?  Do  substances  that 
burn  in  air  burn  more  or  less  vigorously  in  oxygen? 
What  happens  in  the  case  of  the  iron  wire?  Will 
the  wire  burn  in  the  air?  What  can  you  say  in  gen- 
eral about  burning  in  oxygen  as  compared  with  burn- 
ing in  air? 

Ex.  32.  (By  the  Teacher.)  Hollow  the  end  of 
a  piece  of  crayon  into  a  small  cup  and  attach  a  piece 
of  wire  as  shown  in  Fig.  56.  Place  a  piece  of  phos- 
phorus the  size  of  a  grain  of  wheat  in  the  cup  and 
ignite  by  touching  it  with  a  hot  wire.  Lower  it  into 
a  bottle  of  oxygen  and  note  results.  (Phosphorus  burning  phos- 
must  be  handled  with  extreme  care.  It  is  always  p  ° 
kept  covered  with  water  and  should  always  be  cut  under  water.  Never 
touch  phosphorus  with  the  hands,  but  handle  with  forceps.)  How 
does  the  burning  in  air  compare  with  burning  in  oxygen?  What  is 
the  source  of  the  white  fumes  ?  Do  the  white  fumes  dissolve  in  water  ? 


60  INORGANIC  CHEMISTRY 

Ex.  33.  (By  the  Teacher.)  Fill  a  half  pint  cream  bottle  one  third 
full  of  oxygen  and  two  thirds  full  of  hydrogen.  Wrap  the  bottle  in  a 
thick  towel  and  holding  at  arm's  length  quickly  bring  it  mouth  down- 
ward over  a  flame.  How  does  the  explosion  compare  with  that  of 
hydrogen  and  air  ?  What  is  meant  by  the  oxy-hydrogen  flame  ?  How 
does  it  compare  with  other  flames  for  heat?  Draw  a  diagram  of  an 
oxy-hydrogen  burner.  How  is  the  limelight  obtained  ? 

Ex.  34.  What  is  analysis  ?  Synthesis  ?  What  is  an  element  ?  A 
compound?  Give  examples  of  each.  How  does  the  number  of  ele- 
ments compare  with  the  number  of  compounds?  What  is  a  physical 
change?  A  chemical  change?  A  mechanical  mixture?  A  chemical 
compound  ?  With  what  kind  of  changes  is  chemistry  concerned  ? 


CHAPTER  V 
OXYGEN  (Continued} 

36.  Oxides  and  Oxidation.     The  experiments  with  oxy- 
gen described  in  the  last  chapter  show  that  at  ordinary 
temperatures  oxygen  has  little  effect  upon  substances  placed 
in  it,  but  that  at  higher  temperatures  it  makes  them  burn 
more  actively  than  they  will  in  the  air.     Oxygen  is  said, 
therefore,  to  be  rather  inactive  at  low  temperatures,  but 
very  active  at  high  temperatures.     What  really  happens, 
when  the  substances  burn  in  oxygen,  is  that  the  oxygen 
combines  with  the  burning  materials.     Oxygen  unites  with 
sulphur   and    forms   a   suffocating   gas;    with   phosphorus 
it  forms  white  fumes;   and  with  iron  it  forms  the  black 
molten  material  which  drops  to  the  bottom  of  the  bottle. 

When  oxygen  unites  with  another  element,  the  result  is  a 
compound  called  an  oxide.  Thus  iron  and  oxygen  form  iron 
oxide;  phosphorus  and  oxygen  form  phosphorus  oxide. 
Some  of  the  oxides  are  colorless  gases  like  the  oxides  of  sul- 
phur and  carbon,  but  the  majority  of  them  are  solids,  such 
as  the  oxides  of  iron,  phosphorus,  and  lead.  When  oxygen 
unites  with  another  element,  the  process  is  called  oxidation, 
and  the  resulting  compounds  formed  are  known  as  products 
of  oxidation.  Water  is  the  product  of  the  oxidation  of  hydro- 
gen, and  is  in  reality  hydrogen  oxide. 

37.  Burning  in  Air  due  to  Oxygen.     The  strong  resem- 
blance between  the  burning  of  substances  in  oxygen  and  in 

61 


62 


INORGANIC   CHEMISTRY 


the  air  suggests  that  these  two  processes  are  the  same.  More- 
over, carefully  conducted  experiments  show  that  whether 
the  substance  is  burned  in  oxygen  or  in  the  air  the  products 
formed  are  exactly  the  same.  It  is  certain,  therefore,  that 
the  process  of  burning  in  the  air  is  due  to  the  presence  of 
oxygen.  The  fact  that  substances  burn  less  readily  in  air 
than  in  oxygen  further  suggests  that  the  air  is  not  pure  oxy- 
gen. The  proportion  of  oxy- 
gen in  the  air  can  be  shown 
by  a  simple  experiment  (Fig. 
57). 

A  small  piece  of  cork  or  of 
wood  A  is  floated  in  the  water 
in  the  pan  B.  A  piece  of 
phosphorus  the  size  of  a  pea 
is  placed  on  the  cork.  The 
phosphorus  is  ignited  by  a 
touch  from  a  piece  of  hot 
iron  wire,  and  a  wide-mouth  bottle  C  is  carefully  placed 
over  it.  The  phosphorus  will  burn  until  the  oxygen  in  the 
air  within  the  jar  is  exhausted,  and  then  it  will  be  extin- 
guished. The  water  rises  in  the  bottle  to  take  the  place 
of  the  oxygen  consumed.  The  white  cloud  of  oxide  of 
phosphorus  will  soon  be  dissolved  in  the  water,  and  if  the 
bottle  is  so  adjusted  that  the  level  of  the  water  inside  and 
outside  is  the  same,  it  will  be  found  that  the  jar  is  about 
one  fifth  full  of  water.  The  air,  therefore,  is  about  one  fifth 
oxygen  and  four  fifths  of  some  other  gas  which  does  not  unite 
with  the  phosphorus. 

38.  Combustion  Defined.  Combustion,  in  its  ordinary 
sense,  whether  in  oxygen  or  in  the  air,  consists  in  the  union 
of  substances  with  oxygen  with  the  evolution  of  light  and 


FIG.  57.  — Experiment  to  show  propor- 
tion of  oxygen  in  the  air. 


OXYGEN 


63 


heat.1  Substances  which  will  unite  with  oxygen  are  said  to 
be  combustible  and  those  which  will  not  are  incombustible. 
All  the  important  elements  will  unite  with  oxygen. 

39.  Kindling  Temperature.  It  has  been  shown  that 
substances  do  not  usually  combine  with  oxygen  at  ordinary 
temperatures.  This  is  a  fortunate  thing ;  for  if  it  were  not 
so,  all  combustible  substances  in  nature  would  burn  up, 
since  there  is  sufficient  oxygen  in  the  air  for  that  purpose. 
Some  substances  need  to  be  heated  very  little  before  they 
will  burn,  while  others  ignite  only  when  raised  to  very  high 
temperatures.  If  small  pieces  of  phosphorus,  sulphur, 
and  charcoal  are  placed  on  an  iron  plate  with  a  lighted  burner 
beneath,  the  phosphorus  soon  bursts  into  a  flame.  The 
sulphur,  however,  requires  considerable  heat  to  ignite  it, 
and  the  charcoal  does  not  burn  until  it  reaches  red  heat. 
Similar  experiments  with 
a  variety  of  substances 
demonstrate  that  each 
has  a  certain  tempera- 
ture to  which  it  must  be 
heated  before  it  will  ig- 
nite. This  is  known  as 
the  kindling  temperature 
of  the  substance.  When 
the  material  begins  to 
burn,  the  heat  of  the 
burning  parts  raises  the 

temperature  of  the  adjacent  parts  to  the  kindling  tempera- 
ture and  the  burning  spreads.  The  way  the  flame  creeps 

1  Chemists  sometimes  define  combustion  as  "any  rapid  chemical  action 
accompanied  by  light  and  heat."  There  is  a  limited  number  of  such  chemi- 
cal actions  in  which  oxygen  takes  no  part. 


FIG.  58. — The  difference  in  the  kindling 
temperature  of  paper,  wood,  and  coal  is  utilized 
in  building  a  coal  fire. 


64  INORGANIC   CHEMISTRY 

along  a  stick  of  wood  is  an  example  in  point.  Practical 
advantage  is  taken  of  the  difference  in  kindling  tempera- 
tures in  lighting  a  coal  fire,  by  the  fact  that  paper  is  first 
placed  on  the  grate  bars,  then  pine  kindling  is  placed  on  the 
paper,  and  then  the  coal  above  (Fig.  58).  The  paper  is 
easily  ignited,  but  since  it  alone  cannot  raise  the  coal  to 
its  kindling  temperature,  the  pine  is  placed  between. 

40.  Slow  Oxidation.  Some  substances  unite  slowly  with 
oxygen  at  ordinary  temperatures  without  the  evolution 
of  light.  Iron  is  such  a  substance.  When  iron  rusts,  as 
it  does  when  exposed  to  moisture,  the  change  consists  in 
the  union  of  the  iron  with  oxygen,  and  the  rust  is  similar 
to  the  substance  formed  when  iron  is  burned  in  oxygen.  If 
some  moist  iron  dust  or  filings  are  placed  on  the  floating 
cork  shown  in  Fig.  57,  and  the  apparatus  allowed  to  stand 
for  one  or  two  weeks,  the  water  will  be  seen  to  rise  slowly 
in  the  bell  jar.  If  allowed  to  stand  long  enough,  it  will  be 
found  that,  as  in  the  case  of  the  burning  phosphorus,  one 
fifth  of  the  volume  of  the  bottle  is  filled  with  water.  A 
change  of  this  kind  is  known  as  slow  oxidation.  Slow  oxida- 
tion is  of  common  occurrence.  It  is  always  taking  place 
in  the  animal  body.  The  oxygen  taken  into  the  lungs  acts 
upon  various  substances  in  the  body,  oxidizing  them  into 
other  forms  which  can  be  more  readily  eliminated,  as,  for 
example,  water  and  an  oxide  of  carbon.  The  decaying  of 
wood  and  other  vegetable  and  animal  matter  is  a  slow  oxida- 
tion process  brought  about  by  the  action  of  bacteria. 

What  difference  is  there  between  combustion  and  slow 
oxidation  ?  Apparently  in  the  case  of  the  latter  there  is  no 
light  or  heat  produced.  A  careful  study  of  the  subject 
has  shown,  however,  that  a  given  amount  of  iron  produces 
exactly  the  same  amount  of  heat  whether  burned  in  oxygen  or 


OXYGEN 


65 


allowed  to  rust  in  the  air.  In  the  one  case  the  heat  is  all 
given  off  in  a  short  time  and  the  temperature  becomes  so 
high  that  light  is  emitted.  In  the  other  case  the  heat  is 
evolved  slowly,  and  the  surrounding  air  conducts  it  away 
as  rapidly  as  it  is  produced.  The  quantity  of  heat  is  the  same 
in  both  cases. 

41.  Weight  Relations  of  Combustion.  If  the  burning 
of  a  substance  consists  in  its  union  with  oxygen,  it  follows 
that  the  products  of  combustion  must  weigh  more  than  the 
substance  burned.  The  oxide  resulting  from  the  burning 
of  the  iron  wire  weighs  more  than  the  wire  itself.  The  oxide 
produced  when  copper  was  heated  in  oxygen  is  heavier  than 
the  copper  burned.  In  the  case  of  burning  wood,  or  a  lighted 
candle,  there  is  apparently  a  loss  of  matter,  for  the  wood  and 
candle  almost  completely  disappear.  The  wood  and  the 
candle  are  composed 
largely  of  carbon  and 
hydrogen.  When  the 
latter  burns,  it  forms 
the  oxide  of  hydrogen 
called  water  and  dis- 
appears into  the  air 
as  vapor;  but  it  has 
been  shown  that  the 
water  produced 
weighs  nine  times  as 
much  as  the  hydrogen 
burned  (31).  The 

carbon  burns  to  an  oxide  which  is  a  colorless  gas,  and  it  also 
disappears  into  the  atmosphere.  This  gas  weighs  nearly 
four  times  as  much  as  the  carbon  burned.  Figure  59  shows 
a  method  of  demonstrating  that  the  products  of  combus- 

EV.    CHEM. — 5 


FIG.  59.  — Experiment  to  show  the  weight  relations 
of  combustion. 


66  INORGANIC  CHEMISTRY 

tion  of  a  candle  weigh  more  than  the  candle  itself.  Two 
lamp  chimneys  are  suspended  on  each  side  of  a  balance  over 
unlighted  candles.  The  upper  parts  of  the  chimneys  are 
filled  with  caustic  soda  (sodium  hydroxide),  which  has  the 
power  of  absorbing  water  and  the  oxide  of  carbon.  The 
pans  are  exactly  balanced  by  placing  sand  or  small  weights 
on  the  lighter  side.  One  of  the  candles  is  then  lighted,  and 
as  it  burns  away  and  the  products  of  combustion  are  ab- 
sorbed by  the  caustic  soda  in  the  chimney  above  the  burnt 
candle,  that  side  of  the  balance  slowly  sinks,  showing  that 
it  has  increased  in  weight. 

This  experiment  shows  that  the  elements  in  the  candle  were 
not  actually  destroyed,  but  merely  changed  into  other  com- 
pounds by  uniting  with  oxygen.  In  fact,  scientists  believe 
that  matter  cannot  be  destroyed,  and  that  after  every 
physical  or  chemical  change  the  amount  of  matter  is 
the  same  as  before.  This  is  merely  the  equivalent  of 
saying  that  it  is  not  possible  either  to  create  or  destroy 
matter.  This  is  known  as  the  law  of  the  indestructibility 
of  matter,  sometimes  known  as  the  law  of  the  conservation 
of  matter. 

42.  Spontaneous  Combustion.  While  slow  oxidation  usu- 
ally takes  place  in  such  a  way  that  there  is  no  perceptible 
rise  of  temperature,  it  is  possible  for  the  oxidizing  substance 
to  be  so  placed  that  the  heat  cannot  radiate  as  fast  as  formed. 
In  that  case  the  heat  may  accumulate  until  it -has  warmed 
the  material  to  its  kindling  temperature,  upon  reaching  which 
it  will  burn.  This  is  probably  the  cause  of  the  so-called 
spontaneous  combustion.  Some  oils,  notably  linseed  oil, 
oxidize  readily,  and  oily  rags  have  often  been  discovered 
to  be  on  fire.  Barns  have  been  burned  by  the  spontaneous 
combustion  of  hay,  and  fires  that  are  to  be  accounted  for 


OXYGEN 


67 


only  by  spontaneous  combustion  have  been  found  in  the 
center  of  large  heaps  of  coal. 

43.  Reduction  the  Opposite  of  Oxidation.     It  has  been 
said  that  the  union  of  oxygen  with  other  elements  is  called 
oxidation;   but  when  hydrogen  is  passed  over  copper  oxide 
the  opposite  effect  is  produced,  namely,  the  oxygen  is  taken 
away  from  the  copper.     The  process,  which  is  the  reverse 
of  oxidation,  is  known  as  reduction.     Anything  which,  like 
hydrogen,  causes  another  substance  to  lose  oxygen  is  called 
a  reducing  agent.     In  this  experiment  it  will  be  noticed  that 
the. hydrogen  is  oxidized  but  the  copper  oxide  is  reduced. 

44.  Occurrence  of  Oxygen.     Oxygen  is  the  most  abun- 
dant and  most  widely  distributed  of  all  the  elements.     It 
comprises  four  fifths  of  the  water,  one  fifth  of  the  air,  and 
one  half  of  the  rocks  of  the  earth.     It  is 

found  in  all  plant  and  animal  bodies,  and 
it  is  absolutely  essential  to  all  life  of  both 
the  animal  and  vegetable  kingdom.  It  dis- 
solves to  the  extent  of  three  per  cent  in 
water,  making  possible  the  life  of  fishes.  It 
is  used  commercially  in  a  number  of  ways, 
and  it  is  useful  in  the  treatment  of  certain 
diseases.  For  commercial  purposes  it  is  sold 
in  a  compressed  form  in  strong  steel  cylin- 
ders (Fig.  60).  It  is  prepared  from  po- 
tassium chlorate,  or  from  liquid  air  in  the 
manner  to  be  described  in  the  next  chapter. 

45.  Hydrogen  Peroxide.     Water,  as  has 
been  shown,  consists  of  one  part  by  weight 

of  hydrogen  to  eight  of  oxygen.  Another  compound  of 
hydrogen  and  oxygen  is  known  which  contains  twice  as  much 
oxygen  as  water,  —  that  is,  16  parts  by  weight  of  oxygen 


FlG.  60.— A  cyl- 
inder of  commercial 
oxygen. 


68  INORGANIC  CHEMISTRY 

to  one  of  hydrogen.  This  substance  is  known  as  hydrogen 
peroxide.  It  is  an  unstable  compound  and  readily  gives  up 
half  of  its  oxygen  and  changes  to  water.  Thus  it  is  a  good 
oxidizing  agent.  Its  use  in  medicine  and  in  bleaching  de- 
pends upon  this  property.  It  is  never  used  in  the  pure 
state.  The  solution  found  on  the  market  contains  about 
three  per  cent  of  actual  hydrogen  peroxide  dissolved  in 
water. 

EXERCISES 

Ex.  35.  Is  oxygen  very  active  at  low  temperatures?  At  high 
temperatures  ?  What  takes  place  when  substances  burn  in  oxygen  ? 
When  oxygen  unites  with  another  element,  what  is  the  product  called  ? 
Name  the  product  of  the  combustion  of  oxygen  with  iron ;  with  phos- 
phorus ;  with  carbon.  What  is  meant  by  oxidation  ?  What  is  meant 
by  "  products  of  oxidation "  ?  What  is  formed  when  hydrogen  is 
oxidized  ? 

Ex.  36.  (By  the  Teacher.)  Perform  the  experiment  described  in 
paragraph  37. 1  What  causes  the  water  to  rise  in  the  bottle?  What 
proportion  of  the  air  is  oxygen?  Compare  the  burning  in  air  with 
burning  in  oxygen.  Are  the  products  of  combustion  the  same  in 
each  case?  In  which  does  the  burning  take  place  more  vigorously? 
What  is  meant  by  combustion  as  the  term  is  ordinarily  used?  What 
is  meant  by  combustible  and  incombustible  substances? 

Ex.  37.  Perform  the  experiment  described  in  paragraph  39.  What 
happened  to  the  phosphorus,  sulphur,  and  charcoal  ?  Which  ignited 
at  the  lowest  temperature?  What  is  meant  by  kindling  tempera- 
ture? Do  substances  usually  burn  at  ordinary  temperatures?  Why 
is  this  a  fortunate  thing?  Is  there  much  difference  in  the  kindling 
temperatures  of  substances?  Is  the  kindling  temperature  constant 
for  each  substance?  What  practical  use  of  the  difference  in  kindling 
temperatures  of  substances  is  made  in  the  home?  Light  the  end  of 
a  long  splinter  of  wood.  What  makes  the  flame  spread  along  the 

1  Allow  the  bottle  to  remain  standing  mouth  downward  in  the  water  for 
use  in  a  later  experiment. 


OXYGEN 


69 


wood  ?     Why  does  the  wood  burn  more  rapidly  if  held  with  the  burn- 
ing end  downward  than  if  the  burning  end  is  at  the  top  ? 

Ex.  38.  Examine  a  piece  of  rusty  iron  from  your  home.  Of  what 
is  the  rust  composed  ?  How  does  it  compare  with  the  product  formed 
when  iron  burns  in  oxygen  ?  What  is  meant  by  slow  oxidation  ?  Is  it 
of  common  occurrence?  Mention  a  few  instances  of  slow  oxidation. 
What  is  the  source  of  the  heat  in  animal  bodies?  Is  heat  produced 
during  slow  oxidation  ?  How  does  the  quantity  of  heat  compare  with 
that  produced  by  rapid  combustion  of  the  same  substance  ? 

Ex.  39.  Perform  the  experiment  described  in  paragraph  41.  What 
becomes  of  the  candle  when  it  burns  ?  Do  the  products  of  combustion 
weigh  more  or  less  than  the  substance  burned?  When  wood  or  coal 
is  burned  in  the  stove,  only  a  small  amount  of  ash  is  left;  what  be- 
comes of  the  remainder  of  the  fuel  ?  Is  any  of  the  matter  destroyed  ? 
What  is  the  law  of  the  indestructibility  of  matter?  Iron  rust  weighs 
more  than  the  iron  from  which  it  was  made;  has  matter  been  created? 
How  is  spontaneous  combustion  explained?  Why  is  it  dangerous  to 
allow  oily  rags  to  lie  around  ?  Do  you  know  of  any  cases  of  spontaneous 
combustion  in  your  vicinity? 

Ex.  40.  Arrange  apparatus  as  shown  in  Fig.  61.  A  is  an  ordinary 
hydrogen  generator.  B  is  a  piece  of  glass  tubing  with  the  horizontal 
arm  about  8  inches  long.  C  is 
a  hard  glass  test  tube  with  some 
fine  copper  oxide  at  the  closed 
end.  Allow  hydrogen  to  pass 
through  the  tube  for  a  few 
minutes  and  then  continuously 
heat  the  copper  oxide  and  note 
the  result.  Does  the  copper 
oxide  change  color?  Why? 
What  becomes  of  the  oxygen 
which  is  removed  from  the  cop- 
per oxide?  What  is  meant  by  reduction?  Is  hydrogen  a  reducing 
agent  ?  Is  the  copper  oxide  a  reducing  agent  or  an  oxidizing  agent  ? 

Ex.  41.  Tell  what  you  can  about  the  occurrence  of  oxygen,  (a)  in 
the  elemental  form,  (&)  in  combination  with  other  substances.  How 
is  it  prepared  commercially  ?  What  is  hydrogen  peroxide  ?  For  what 
is  it  used? 


FIG.  61.  —  Reducing  copper  oxide  with 
hydrogen. 


CHAPTER  VI 


AIR  —  NITROGEN 

46.  IT  will  be  well  to  return  to  the  experiment  in  which 
phosphorus  was  burned  in  the  wide-mouth  bottle  (Fig.  57). 
The  bottle  is  now  so  adjusted  that  the  level  of  the  water 
inside  and  outside  is  the  same,  a  glass  plate 
is  slipped  under  the  mouth,  and  the  bottle 
turned  mouth  upward.  If,  now,  a  lighted 
candle  is  placed  in  the  bottle  (Fig.  62),  it 
will  not  burn  as  it  does  in  air  or  oxygen,  but 
will  be  immediately  extinguished.  Nor  will 
the  gas  itself  burn  as  does  hydrogen.  Here 
is  a  new  gas,  then,  which  neither  burns  nor 
supports  combustion.  This  gas  was  first 
studied  by  the  English  chemist  Rutherford 
in  1772.  It  was  later  named  nitrogen  be- 
cause of  its  presence  in  niter  or  saltpeter. 

47.   Properties.     Nitrogen  is  a   colorless, 
odorless,  and  tasteless  gas.     It  is  lighter  than 

FIG.    62.  —  A 

candle    is    extin-   oxygen  or   air  and  constitute3    nearly  four 


fifths  of  the  atmosphere.  It  is  less  soluble 
in  water  than  is  oxygen.  Chemically  it  is 
said  to  be  very  inactive,  for  it  will  not  readily  unite  with  any 
other  element,  even  at  rather  high  temperatures.  It  is  evi- 
dent that  it  does  not  unite  with  oxygen  at  ordinary  tem- 
peratures. The  electric  spark  will  cause  a  limited  union 
of  nitrogen  and  oxygen,  and  this  combination  is  supposed 

70 


AIR  —  NITR  OGEN  71 

to  take  place  to  a  slight  extent  during  electric  storms.  It 
may  be  said,  therefore,  that  most  of  its  properties  are  of  a 
negative  character,  and  that  nitrogen  is  most  noted  in  the 
laboratory  for  what  it  will  not  do.  Animals  placed  in  nitro- 
gen die  immediately  of  suffocation,  not  because  the  gas  is 
poisonous,  but  because  they  cannot  live  without  oxygen. 

48.  Occurrence.     Nitrogen  exists  as  an  element  in  the 
atmosphere.     United  with  other  elements  into  very  com- 
plex compounds,  it  is  found  in  plant  and  animal  tissues. 
It  is  sometimes  said  to  be  the  most  important  element  to 
life,  as  it  is  necessary  to  the  formation  of  the  protoplasm  of 
the  cell  upon  which  life  depends.     While  the  worker  in  the 
laboratory  finds  difficulty  in  making  nitrogen  combine  with 
other  elements,  nature  has  a  way  of  bringing  about  this 
union.     Certain  bacteria  found  in  the  soil  have  the  power 
of  combining  nitrogen  with  hydrogen  and  oxygen  in  such  a 
way  that  crops  can  use  it.     Some  of  these  bacteria  grow  in 
little  nodules,  or  tubercles,  on  the  roots  of  plants  like  the 
clovers,  peas,  beans,  and  other  leguminous  plants.     Others 
of  these  bacteria  do  not  grow  on  the  roots  of  plants  but  live 
free  in  the  soil.     Animals  eat  the  crops  and  get  their  neces- 
sary nitrogen  compounds  in  that  way,  so  that  these  tiny 
bacteria  are  responsible  for  most  of  the  combined  nitrogen 
found  in  nature.     More  will  be  said  about  these  bacteria 
later  (168). 

49.  Air   a   Mechanical   Mixture.     The   ratio    between 
nitrogen  and  oxygen  in  the  air  is  so  nearly  constant  that 
the  question  might  arise  whether  it  is  a  compound  or  a 
mechanical  mixture  of  these  two  elements.     All  experiments 
indicate  that  the  air  is  merely  a  mechanical  mixture  consist- 
ing of  practically  21  per  cent  oxygen,  78  per  cent  nitrogen, 
and  1  per  cent  of  small  quantities  of  a  number  of  other 


72  INORGANIC  CHEMISTRY 

gases.  Two  reasons  for  this  belief  may  be  mentioned. 
First,  true  chemical  compounds  do  not  vary  in  the  least  in 
composition.  The  variation  in  the  composition  of  air, 
though  slight,  is  sufficient  to  show  that  it  is  not  a  compound. 
Second,  if  air  is  dissolved  in  water  and  the  air  taken  out  of 
the  water  by  means  of  an  air  pump,  it  will  be  found  that  the 
ratio  of  oxygen  to  nitrogen  in  this  air  is  as  1  to  2,  while  in 
the  atmosphere  it  is  as  1  to  4.  The  ratio  of  the  elements  in 
a  true  chemical  compound  does  not  change  when  the  sub- 
stance is  dissolved  in  water. 

50.  Air  Contains  Water  Vapor.  The  experiment  wherein 
calcium  chloride  absorbed  moisture  from  the  air  shows  that 
the  atmosphere  contains  water  vapor.  This  is  also  dem- 
onstrated when  moisture  collects  on  a  vessel  containing 
cold  water.  The  surrounding  air  is  cooled 
to  such  an  extent  that  some  of  its  moisture 
is  deposited  on  the  cold  vessel  in  the  form 
of  liquid  water  (Fig.  63). 

The  amount  of  moisture  in  the  atmos- 
phere is  the  most  variable  of  all  its  con- 
stituents and  is  known  as  humidity.    The 
power  of  the  air  to  hold  water  vapor  in- 
FIG. 63.— Moisture     creases  with  rise  of  temperature.     When 

collects  on  the  outside 

of  a  vessel  of  cold  air  contains  all  the  moisture  it  will  hold,  it 
is  said  to  be  saturated.  At  10°  C.  one  cubic 
meter  of  air  will  hold  9.7  grams  of  water  vapor,  while  at 
20°  C.  it  takes  17.1  grams  to  saturate  it.  Relative  humidity, 
a  term  quite  commonly  used,  is  the  ratio  between  the  amount 
of  water  vapor  in  the  air  at  a  given  temperature  and  the 
amount  it  could  hold  when  saturated  at  that  temperature. 
A  relative  humidity  of  80,  for  instance,  means  that  the  air 
contains  80  per  cent  of  the  moisture  it  is  possible  for  it  to 


AIR  — NITROGEN 


73 


hold  at  that  temperature.  When  the  air  is  saturated,  the 
relative  humidity  is  said  to  be  100.  As  air  cools,  its  power 
to  hold  moisture  decreases,  and  finally  the  water  vapor  con- 
denses as  dew.  The  temperature  at  which  this  takes  place 
is  known  as  the  dew  point. 

51.  Air  Contains  Carbon  Dioxide.  If  a  dish  contain- 
ing limewater  is  allowed  to  stand  exposed  to  the  air  for  a 
short  time,  a  crust  of  white  material  , 

forms  on  the  surface.  This  effect  is  not 
produced  by  pure  oxygen,  by  nitrogen,  or 
by  water.  If  the  mouth  is  placed  near  a 
dish  of  limewater  and  the  breath  blown  on 
it,  or  if  a  lighted  candle  is  lowered  into  a 
wide-mouth  bottle  containing  a  little  lime- 
water  (Fig.  64),  the  white  crust  forms  very 
rapidly.  Evidently,  then,  the  air  contains 
another  gas  which  is  probably  identical 
with  some  substance  found  in  the  breath, 
and  which  is  also  formed  when  a  candle 
burns.  This  is  a  compound  of  oxygen  and 
carbon  known  as  carbon  dioxide,  commonly  called  carbonic 
acid  gas.  This  gas  will  be  more  fully  discussed  in  the 
chapter  on  carbon  compounds. 

The  amount  of  carbon  dioxide  in  the  air  is  very  small, 
amounting  to  only  0.03  per  cent  or  3  parts  in  10,000  in  the 
country,  and  seldom  exceeding  0.06  per  cent  in -the  cities 
where  much  coal  is  burned.  Small  as  the  quantity  is,  it  is 
very  important ;  for  without  it  green  plants  could  make  no 
growth.  The  amount  in  the  air  is  practically  constant;  for 
plants  use  it  at  about  the  same  rate  at  which  it  is  produced 
by  the  breathing  of  animals,  by  the  burning  of  wood  and 
coal,  and  by  other  oxidation  processes  (107). 


FIG.  64.  —  A  burn- 
ing candle  lowered 
into  a  bottle  contain- 
ing limewater. 


74 


INORGANIC  CHEMISTRY 


52.  Traces  of  Other  Substances  in  Air.     In  addition  to 
the  four  substances  mentioned,  the  atmosphere  contains 
small  quantities  of  certain  rare  gases  and  traces  of  sulphur 
compounds,   as  well  as  dust,   bacteria,   and  various  sub- 
stances given  off  from  the  lungs. 

53.  Diffusion  of  Gases.     Before  leaving  the  subject  of  air 
it  will  be  well  to  learn  something  of  those  physical  prop- 
erties of  gases  to  which  occasional  reference  must  be  made. 

Gases  diffuse  in  all  directions  regardless  of 
their  density.  If  two  bottles  (Fig.  65)  are 
placed  mouth  to  mouth,  the  upper  one  con- 
taining the  light  gas,  hydrogen,  and  the 
lower  containing  air,  which  is  fourteen  times 
as  heavy,  diffusion  begins  immediately,  and 
after  a  few  minutes  there  is  hydrogen  in  the 
lower  bottle  and  air  in  the  upper.  If  it  were 
not  for  this  property  of  gases,  the  atmos- 
phere would  consist  of  a  lower  layer  of  the 
heavy  carbon  dioxide,  a  middle  layer  of 
oxygen,  and  an  upper  one  of  nitrogen,  which 
is  the  lightest  of  the  three  gases.  Diffusion 
keeps  the  gases  uniformly  mixed,  but  in  the 
atmosphere  this  process  is  accelerated  by  the 
mixing  action  of  the  winds  and  other  air  currents. 

54.  Effect  of  Temperature  and  Pressure.     Substances1 
expand  when  heated,  but  gases   are   affected  to   a   much 
greater   extent   than   liquids   or   solids.     That   heated   air 
expands  and  is,  therefore,  lighter  than  cold  air  is  shown 
by  the  hot-air  balloon  so  commonly  seen  at  the  country 
fairs.     Gases  respond  readily  to  change  of  pressure.     The 
volume  of  a  gas  is  inversely  proportional  to  the  pressure  to 

1  Water  below  4°  C.  is  an  exception. 


FIG.  65.  —  To 
show  the  diffusion 
of  gases. 


AIR  — NITROGEN 


75 


which  it  is  subjected.  If  the  pressure  is  doubled,  the  volume 
of  the  gas  becomes  one  half,  provided  the  temperature  re- 
mains unchanged.  While  different  liquids  and  solids  ex- 
pand or  contract  at  varying  rates  upon  change  of  tempera- 
ture or  pressure,  it  is  interesting  to  note  that  all  gases  behave 
the  same  regardless  of  their  composition. 

55.  Liquefaction.     All  gases  can  be  condensed  to  liquids 
and  even  to  solids,  provided  the  proper  combination  of 
very  low  temperature  and  high  pressure  can  be  secured. 
Oxygen  cannot  be  condensed  to  a  liquid  unless  its  temper- 
ature is  lowered  to  —  119°  C.,  while  nitrogen  must  be  cooled 
to  -  146°  C.  and  hydrogen  to  -  241°  C.    Air  can  be  liquefied 
in  the  same  way,  and  when  it  changes  back  to  the  gaseous 
form  the  nitrogen  boils  off  first,  leaving  the  oxygen  behind. 
Oxygen  of  95  per  cent  purity  is  prepared  commercially  in 
this   way.      This  behavior  of  liquid   air   is 

another  proof  that  air  is  a  mechanical  mix- 
ture. 

56.  Gases    Are  Substances.     That  gases 
are  matter  and  actually  occupy  space  can  be 
shown  by  a  simple  experirrent.     A  bottle  of 
air  or  some  other  gas  is  fitted  with  a  tight 
cork  carrying  a  funnel  with  a  small  opening, 
as  in  Fig.  66.     If  the  apparatus  is  air-tight, 
water  poured  in  the  funnel  will  not  run  into 
the  bottle,  a  circumstance  which  shows  that 
the  bottle   is  already  full.     If  the   cork  is 
loosened  to  allow  the  gas  to  escape,  the  water 
will  enter  the  bottle. 

That  gases  have  weight  also  may  be  shown  by  weighing 
a  flask  from  which  the  air  has  been  exhausted  by  an  air 
pump,  and  then  weighing  the  flask  when  filled  with  dif- 


FiG.66.— The 
air  in  the  bottle 
prevents  the  water 
in  the  funnel  from 
entering. 


76  INORGANIC  CHEMISTRY 

ferent  gases.     A  liter  (about  one  quart)  of  hydrogen  weighs 
0.09  gram,  while  a  liter  of  oxygen  weighs  1.43  grams. 


EXERCISES 

Ex.  42.  Adjust  the  bottle  left  from  Ex.  37  so  that  the  level  of  the 
water  inside  and  outside  of  the  bottle  is  the  same.  Slip  a  glass  plate 
over  the  mouth  of  the  bottle  and  turn  it  mouth  upward.  Lower  a 
lighted  candle  into  the  bottle.  Does  the  candle  continue  to  burn? 
Does  the  gas  in  the  bottle  ignite?  Is  the  gas  in  the  bottle  different 
from  the  two  previously  studied?  What  is  the  name  of  this  gas? 
Give  the  properties  of  nitrogen.  Is  nitrogen  an  element  or  a  com- 
pound? What  can  you  tell  about  the  occurrence  of  nitrogen?  How 
doe?  nature  cause  nitrogen  to  combine  with  other  elements  ?  How  do 
animals  get  their  nitrogen  compounds?  Is  air  a  chemical  compound 
or  a  mechanical  mixture?  Give  reasons  for  your  answer. 

Ex.  43.  Have  you  ever  noticed  moisture  gather  on  the  outside  of 
a  vessel  containing  cold  water?  Where  does  this  moisture  come 
from  ?  In  what  other  way  can  you  demonstrate  the  presence  of  water 
vapor  in  the  air?  What  is  meant  by  the  humidity  of  air?  What  is 
the  meaning  of  relative  humidity?  When  is  the  relative  humidity 
said  to  be  100  ?  If  air  was  suddenly  heated  or  cooled,  would  its  relative 
humidity  be  changed  ?  Explain.  What  is  meant  by  the  dew  point  ? 

Ex.  44.  Place  limewater  in  a  shallow  dish  and  allow  it  to  stand 
exposed  to  the  air.  What  happens  to  it?  Blow  the  breath  into  a 
bottle  containing  limewater.  Lower  a  candle  into  a  similar  bottle. 
What  change  takes  place  in  the  limewater?  Does  the  air  contain 
something  that  is  also  found  in  the  breath  and  in  the  products  of  com- 
bustion of  the  candle  ?  What  is  this  substance  ?  Is  much  of  it  present 
in  the  air?  At  home  try  placing  a  dish  of  limewater  outdoors  and 
another  in  the  house  (in  cool  weather  when  the  windows  are  closed) 
and  note  if  there  is  any  difference  in  the  rate  at  which  the  white  crust 
appears  in  the  two  dishes.  What  other  substances  are  found  in  the 
air  besides  nitrogen,  oxygen,  water  vapor,  and  carbon  dioxide? 

Ex.  45.  Fill  an  eight-ounce  bottle  with  hydrogen  and  carefully 
place  it  mouth  downward  over  another  bottle  filled  with  air  as  shown  in 
Fig.  65.  After  letting  it  stand  some  time  slip  a  glass  plate  between  the 


AIR  — NITROGEN  77 

bottles  and  remove  the  upper  one.  Invert  the  lower  bottle  and  quickly 
apply  a  burning  splint  to  the  mouth.  Have  you  any  evidence  that 
some  of  the  lighter  hydrogen  has  passed  downward  into  the  lower 
bottle  ?  What  is  meant  by  diffusion  of  gases  ?  What  effect  does  this 
property  of  gases  have  on  the  composition  of  the  atmosphere  ?  Do  air 
currents  assist?  What  effect  does  pressure  have  on  gases?  How 
are  gases  affected  by  changes  in  temperature  ?  Would  a  hot-air  furnace 
heat  the  house  as  well  if  placed  in  the  garret  instead  of  in  the  basement  ? 
Why  ?  Should  ice  be  placed  in  the  bottom  or  in  the  top  of  a  refriger- 
ator ?  Why  ?  What  makes  the  hot-air  balloon  rise  ?  What  conditions 
are  necessary  to  liquefy  a  gas  ?  When  liquid  air  is  boiled,  which  gas 
boils  off  first  ?  Is  any  practical  use  made  of  this  fact  ? 

Ex.  46.  Fit  a  funnel  with  a  small  opening  into  a  cork  and  place  it 
in  a  bottle  as  in  Fig.  66.  Pour  water  into  the  funnel.  Why  does  the 
water  not  run  into  the  bottle  ?  What  happens  if  you  loosen  the  cork  ? 


CHAPTER  VII 
SULPHUR 

57.  SULPHUR  is  a  well-known  article  of  commerce  in  the 
form  of  roll  sulphur,  or  brimstone,  and  as  the  yellow  powder 
called  flowers  of  sulphur.  It  is  an  element,  but  unlike  those 


FIG.  67.  —  A  solid  block  of  Louisiana  sulphur.  Molten  sulphur  is  pumped 
from  wells  into  immense  wooden  bins,  where  it  solidifies.  It  is  then  broken 
by  blasting  and  loaded  on  freight  cars  for  shipment. 

studied  so  far,  is  a  solid  and  not  a  gas.  It  has  been  known 
from  the  earliest  times  because  it  occurs  abundantly  in 
nature  in  the  elementary  form.  It  is  found  in  the  neigh- 
borhood of  volcanoes,  especially  those  of  Sicily,  which 

78 


SULPHUR  79 

country  was  formerly  the  chief  source  of  the  sulphur  of 
commerce.  Recently  large  deposits  of  sulphur  have  been 
discovered  in  a  number  of  places  in  the  United  States.  The 
state  of  Louisiana  (Fig.  67)  is  the  chief  producer  at  the 
present  time. 

58.  Preparation.     Sulphur  as  found  in  nature  is  mixed 
with  earthy  matter.     If  the  ore  is  heated  until  the  sulphur 
melts,  the  sulphur  may  be  drawn  off  in  a  liquid  form,  leav- 
ing the  stones  and  earth  behind.     The  crude  sulphur  thus 
obtained  is  purified  by  distillation.     The  sulphur  is  distilled 
into  large  cooling  chambers  of  brick.     When   the   vapor 
first  enters  the  condensing  chamber,  it  is  suddenly  cooled 
and  is  deposited  as  the  fine  powder  known  as  flowers  of 
sulphur.     When  the  chamber  becomes  warmer,  the  vapor 
condenses  in  the  form  of  a  liquid,  which  is  drawn  off  from 
the  bottom  of  the  chamber  and  is  molded  in  wooden  molds 
into  the  form  of  roll  sulphur. 

59.  Properties.     Sulphur  is  a  yellow,  brittle  substance. 
It  is  insoluble  in  water,  but  will  dissolve  readily  in  the 
liquid  known  as  carbon  bisulphide.     It  behaves  very  pe- 
culiarly when   heated.      When    the    temperature    reaches 
114.5°  C.,  the  sulphur  melts,  forming  a  thin,  straw-colored 
liquid.     As  the  heat  increases,  the  mass  becomes  darker  in 
color,  and  at  200°  to  250°  C.  it  becomes  so  thick  that  the 
vessel  in  which  it  is  heated  can  be  turned  upside  down  and 
the  sulphur  will  not  run  out.     Finally,  it  again  becomes 
liquid,  and  at  448.4°  C.  it  boils  and  is  converted  into  a 
brownish  yellow  vapor. 

60.  Different  Forms  of  Sulphur.     If  sulphur  is  dissolved 
in  carbon  bisulphide  and  the  clear  liquid  is  poured  off  and 
is  allowed  to  evaporate  slowly,  crystals  of  sulphur  (Fig.  68) 
will  be  formed,  which,  when  examined  through  a  magnifying 


80 


INORGANIC  CHEMISTRY 


FlG.  68.  — Rhombic  or  eight-sided  sulphur  crystals. 


glass,  are  seen  to  be  eight-sided.     This  is  the  form  of  sulphur 
found  in  nature.     If  sulphur  that  has  been  gently  heated  to 

the  melting  point  is 
allowed  to  cool  until 
it  is  about  half  so- 
lidified, the  solid  part 
remaining  after  the 
liquid  is  poured  off 
is  found  to  be  in 
the  form  of  long 
needlelike  crystals 
quite  different  from 
those  described 
above  (Fig.  69). 

On  the  other  hand, 

if  sulphur  is  heated  to  the  boiling  point,  and  the  liquid  is 
poured  in  a  thin  stream  into  cold  water  (Fig.  70),  it  forms 
a  plastic  mass,  entirely  different  in  appearance  from  either 
of  the  other  forms,  and  with  no  crystalline  appearance. 
This  is  known  as 
plastic,  or  amorphous, 
sulphur. 

Neither  the  needle- 
like  (prismatic)  sul- 
phur nor  the  plastic 
sulphur  is  stable, 
because  each,  upon 
standing,  gradually 
changes  over  into  FIQ  6Q  _  prismatic  or  needlelike  sulphur  crystals 
the  eight-sided  form. 

The    greater  stability  of  this  eight-sided  sulphur  explains 
why  it  is  the  form  found  in  nature. 


SULPHUR  81 

Still  another  form  of  sulphur  is  known.  This  is  found 
sometimes  in  sulphur  springs,  but  is  generally  obtained  by 
precipitating  sulphur  from  some 
of  its  compounds.  It  is  almost 
white  in  color  and  is  known  as 
milk  of  sulphur  or  lac  sulphur. 
It  is  used  in  medicine. 

It  will  thus  be  seen  that  sul- 
phur can  exist  in  several  very 
different  forms.  Each  of  these 
forms,  however,  consists  of  sul- 
phur and  nothing  else.  These 
are  known  as  allotropic  forms  of  FIG.  70.  —  The  formation  of 

rr,,  p        .  amorphous  sulphur. 

sulphur.     The  property  ot  exist- 
ing in  different  forms  is  known  as  allotropy  from  two  Greek 
words  meaning  simply  "  another  form." 

61.  Sulphur  Found  in  Compounds.     In  addition   to  its 
occurrence  in  the  elementary  condition  sulphur  is  found 
in  many  compounds.     It  occurs  in  the  water  of  sulphur 
springs,  in  the  air  near  volcanoes,  and  in  many  minerals. 
It  is  found  in  many  plant  and  animal  tissues.     It  is  used 
as  an  insecticide  and  as  a  fungicide.     It  is  an  ingredient  of 
gunpowder  and  of  fireworks,  and  is  used  in  the  manufacture 
of  hard  and  vulcanized  rubber.     Its  most  important  use  is 
in  the  manufacture  of  sulphuric  acid,  one  of  the  most  im- 
portant of  chemical  substances. 

62.  Sulphides.     Sulphur  somewhat  resembles  oxygen  in 
its    chemical    behavior,    especially    toward    metals.      Like 
oxygen  it  unites  slowly  with  some  metals  at  ordinary  tem- 
peratures.    Like   oxygen,    also,    it   readily   combines   with 
most  metals  at  high  temperatures,  as  can  be  shown  in  the 
following  experiment.     Four  grams  of  flowers  of  sulphur 

EV.  CHEM.  —  6 


82  INORGANIC  CHEMISTRY 

and  seven  grams  of  fine  iron  filings  are  thoroughly  mixed 
by  rubbing  in  a  mortar.  That  this  is  only  a  mechanical 
mixture  may  be  shown  by  taking  a  portion  of  the  mixture 
and  drawing  the  iron  out  with  a  magnet,  or  by  dissolving 
out  the  sulphur  with  carbon  bisulphide.  Another  portion 
of  the  mixture  is  placed  in  an  old  test  tube  and  heated 
over  the  Bunsen  burner.  As  soon  as  the  mass  begins  to 
glow,  it  is  removed  from  the  flame.  If,  when  it  is  cold,  the 
tube  is  broken  and  its  contents  are  examined,  it  will  be 
found  that  the  magnet  does  not  attract  the  iron  in  the  mass, 
and  that  sulphur  cannot  be  dissolved  from  it  by  carbon  bi- 
sulphide. The  sulphur  has  combined  chemically  with  the 
iron,  and  an  entirely  new  substance,  known  as  iron  sulphide, 
has  been  formed.  Copper,  lead,  and  other  metals  will 
combine  with  sulphur  in  the  same  way.  The  compound 
formed  by  the  union  of  sulphur  with  another  element  is  called 
a  sulphide,  just  as  that  formed  by  the  union  of  oxygen  and 
another  element  is  called  an  oxide.  Sulphides  are  abun- 
dant in  nature  and  many  of  them  are  valuable  ores.  Lead, 
copper,  mercury,  and  zinc  are  among  the  metals  found  in 
nature  as  sulphides.  The  black  substance  which  forms  on  a 
silver  spoon  that  has  been  allowed  to  remain  in  contact  with 
an  egg  is  silver  sulphide,  the  sulphur  coming  from  the  egg. 
Nearly  all  sulphides  are  insoluble  in  water. 

63.  Sulphur  Dioxide.  In  the  study  of  oxygen  it  was 
shown  that  sulphur  burns,  forming  a  suffocating  gas.  Even 
the  sulphides  of  the  metals  will  burn  if  heated,  both  the 
sulphur  and  the  metal  uniting  with  oxygen  and  yielding 
the  gaseous  oxide  of  sulphur  just  mentioned,  and  the  oxide 
of  the  metal.  Copper  sulphide,  for  instance,  when  burned 
becomes  copper  oxide,  the  sulphur  which  was  combined 
with  the  copper  uniting  with  oxygen  to  form  a  gas.  This 


SULPHUR  83 

gas  has  been  named  sulphur  dioxide  for  reasons  to  be  ex- 
plained shortly. 

Sulphur  dioxide  is  a  colorless  gas  with  a  suffocating  odor. 
It  is  2.21  times  heavier  than  air.  It  can  readily  be  con- 
densed to  a  liquid.  It  will  not  burn  nor  support  combustion. 
In  the  presence  of  moisture  it  bleaches  many  organic  dyes. 
Flowers  and  moistened  pieces  of  cloth  colored  with  vegetable 
dyes  placed  in  a  bottle  in  which  sulphur  is  burned  will  lose 
their  color.  Sulphur  dioxide  is  used  to  bleach  silk,  wool, 
straw,  and  some  other  fibers  which  would  be  injured  by 
some  of  the  more  powerful  bleaching  agents.  It  has  been 
largely  used  as  an  antiseptic  and  disinfectant,  as  it  will  kill 
bacteria.  A  .common  method  of  disin- 
fecting after  illness  is  to  burn  sulphur  in 
the  closed  room.  The  sulphur  candle 
(Fig.  71)  in  which  the  brimstone  is 
molded  around  a  wick  is  a  convenient 
form  to  use  for  this  purpose.  As  a  disin- 
fectant it  is  now  largely  replaced  by  for- 
maldehyde, however,  which  does  not  FlG-  7lc'a^j^  sulphur 
destroy  the  colors  of  the  materials  disin- 
fected, nor  injure  the  metal  of  the  gas  or  electric  fixtures, 
and  other  hardware.  Sulphur  dioxide  has  also  been  used  in 
preserving  fruits  and  other  food  products  since  it  prevents 
fermentation ;  but  the  use  of  this  substance  in  anything  that  is 
to  be  eaten  is  objectionable.  Sulphur  dioxide  is  injurious  to 
plants,  and  it  is  not  unusual  to  find  trees  and  other  vegeta- 
tion completely  destroyed  in  the  vicinity  of  the  smelting 
works  where  the  sulphide  ores  are  being  roasted  to  burn 
off  the  sulphur. 

64.   Sulphur  Trioxide.     Sulphur  dioxide  has  been  found, 
upon  analysis,  to  contain  equal  parts  by  weight  of  sulphur 


84 


INORGANIC  CHEMISTRY 


FIG.  72.  —  Preparation  of  sulphur  trioxide. 


and  oxygen.  Under  ordinary  circumstances  the  sulphur 
dioxide  does  not  readily  take  on  any  more  oxygen.  If, 
however,  sulphur  dioxide  and  oxygen  are  passed  over  finely 
divided  platinum  which  is  highly  heated,  a  new  compound 
of  sulphur  and  oxygen  will  be  formed  which  contains  one  part 
of  sulphur  to  one  and  one  half  parts  of  oxygen,  or  one  half 

imore    oxygen  than 
A is  found  in  sulphur 

.^,,-Q—  Hm^SMS^  ^^         D          i-        •  i  ™   • 

s^£=  dioxide.  This  com- 
pound is  a  colorless 
liquid  which  solidi- 
fies at  about  15°  C., 
and  has  been  named 
sulphur  trioxide.  It 
may  be  prepared 
on  a  small  scale  by  means  of  the  apparatus  shown  in  Fig.  72. 
The  finely  divided  platinum  is  prepared  -by  moistening 
asbestos  fiber  with  a  solution  of  platinum  chloride  and 
igniting  it  in  a  flame.  The  platinum-asbestos  is  placed  in 
the  hard  glass  tubing  at  A.  Air,  to  furnish  oxygen,  is 
introduced  at  B,  and  sulphur  dioxide  at  C.  The  tube  and 
asbestos  are  heated  with  a  Bunsen  burner,  and  the  fumes 
of  sulphur  trioxide  will  be  seen  escaping  into  the  air  at  D. 
It  may  be  condensed  to  a  liquid  if  conducted  into  a  test 
tube  surrounded  with  a  freezing  mixture  of  ice  and  salt. 

It  is  to  be  noted  that  the  platinum  itself  apparently  does 
not  take  part  in  the  chemical  change,  but  in  some  unex- 
plainable  way  causes  the  union  of  the  oxygen  and  sulphur 
dioxide  to  take  place  very  readily.  Substances  like  this, 
which  hasten  what  would  otherwise  be  slow  chemical  changes, 
are  called  catalytic  agents  or  catalyzers,  and  the  action  is 
called  catalysis.  A  catalyzer,  then,  merely  increases  the 


SULPHUR  85 

speed  of  the  chemical  change  but  does  not  alter  its 
products. 

65.  Sulphuric  Acid.  Sulphur  trioxide  unites  very  vig- 
orously with  water.  When  exposed  to  the  air  it  fumes 
strongly,  and  if  thrown  upon  water  it  hisses  like  hot  iron. 
When  sulphur  trioxide  unites  with  water,  the  product  is 
sulphuric  acid,  sometimes  called  oil  of  vitriol.  At  the 
present  time  most  of  the  sulphuric  acid  is  manufactured  by 
a  method  in  which  sulphur  trioxide  is  first  prepared  by  a 
process  similar  to  the  one  described.  Usually  the  sulphur 
dioxide  is  obtained  by  burning  pyrites,  which  is  a  sulphide 
of  iron.  The  sulphur  dioxide  and  air  are  conducted  into 
towers  in  which  the  formation  of  sulphur  trioxide  is  brought 
about  by  means  of  platinum  or  some  other  catalyzer,  and 
the  sulphur  trioxide  is  then  united  with  water  to  form  sul- 
phuric acid.  This  is  known  as  the  contact  method  of  making 
sulphuric  acid.  Another  method  will  be  mentioned  in 
Chapter  X. 

Sulphuric  acid  is  probably  the  most  important  of  all 
manufactured  chemicals.  It  is  the  most  common  reagent 
of  the  chemical  laboratory ;  and  is  used  in  many  industries, 
especially  in  the  manufacture  of  fertilizers,  soda,  aniline 
dyes,  and  nitroglycerin,  and  in  the  refining  of  petroleum. 
Over  four  million  tons  of  sulphuric  acid  are  produced 
annually. 

When  sulphuric  acid  is  pure  it  is  a  colorless,  odorless, 
oily  liquid.  It  is  almost  twice  as  heavy  as  water,  having  a 
specific  gravity  of  1.84.  It  unites  with  water  with  great 
evolution  of  heat.  For  this  reason  great  caution  must  be 
observed  in  mixing  sulphuric  acid  and  water.  The  acid 
should  be  poured  slowly  into  the  water  with  constant  stir- 
ring. The  water  should  never  be  poured  into  the  acid,  for 


86  INORGANIC  CHEMISTRY 

the  great  amount  of  heat  liberated  is  likely  to  cause  an 
explosion  which  will  throw  the  acid  out  of  the  container. 
Sulphuric  acid  exposed  to  the  air  absorbs  water  vapor  until 
it  becomes  quite  dilute.  It  is,  therefore,  a  good  drying 
agent  and  is  often  used  to  dry  gases.  It  destroys  plant 
and  animal  tissue,  for  it  abstracts  hydrogen  and  oxygen  from 
them  in  proportions  to  form  water,  leaving  behind  a  black 
charred  mass  which  is  largely  carbon.  The  painful  burns 
caused  by  sulphuric  acid  are  due  to  this  action.  It  is  also 
sometimes  used  as  an  oxidizing  agent,  for  under  certain  con- 
ditions it  will  give  up  part  of  its  oxygen  to  another  substance. 

In  very  dilute  solutions  sulphuric  acid  has  a  sour  taste. 
If  a  piece  of  blue  litmus  paper,  a  paper  colored  with  a  veg- 
etable dye  called  litmus,  is  placed  in  it,  the  paper  will  turn 
red.  The  sour  taste  and  the  effect  on  litmus  are  properties 
that  are  characteristic  of  a  large  group  of  chemical  com- 
pounds which  are  known  as  acids. 

66.  Sulphuric  Acid  Forms  Salts.  Sulphuric  acid  con- 
tains sulphur,  oxygen,  and  hydrogen,  for  it  is  produced  by 
the  combination  of  sulphur  trioxide  with  water.  In  Chapter 
III,  in  the  discussion  of  the  preparation  of  hydrogen,  it  was 
shown  that  the  hydrogen  could  be  liberated  from  sulphuric 
acid.  It  will  be  well  now  to  consider  what  became  of  the 
other  elements  in  the  acid. 

It  was  noticed  that  while  hydrogen  was  being  evolved 
the  zinc  disappeared.  If  the  liquid  in  the  hydrogen  generator 
is  now  filtered  to  remove  the  black  particles  which  are 
due  to  impurities  in  the  zinc,  and  is  then  slowly  evaporated 
in  a  porcelain  dish  placed  in  a  sand  bath,  the  residue  is  a 
white  solid  which  looks  somewhat  like  common  salt.  If 
this  material  is  redissolved  in  a  small  quantity  of  hot  water 
and  set  aside  for  some  time,  clear  crystals  are  formed.  This 


SULPHUR  87 

substance  contains  the  zinc  which  disappeared  and  the 
sulphur  and  oxygen  which  were  in  the  sulphuric  acid.  It  is- 
a  compound  known  as  zinc  sulphate.  If  iron  is  used  instead 
of  zinc,  the  residue  is  the  green  material  sold  under  the 
name  of  copperas,  which  is  in  reality  iron  sulphate,  and 
consists  of  iron,  sulphur,  and  oxygen. 

What  has  really  happened  in  these  cases,  then,  is  that  the 
zinc  or  iron  has  replaced  the  hydrogen  which  was  in  the  sul- 
phuric acid.  A  compound  formed  by  replacing  the  hydrogen 
of  sulphuric  acid  with  a  metal  is  called  a  sulphate.  Some  of 
the  sulphates  like  zinc  sulphate  and  iron  sulphate  can  be 
made  by  the  action  of  the  acid  on  the  metal,  but  other  metals 
are  not  readily  acted  upon  by  sulphuric  acid.  The  sul- 
phates of  nearly  all  metals,  however,  can  be  made  by  in- 
direct methods ;  namely,  by  the  action  of  sulphuric  acid  on 
the  oxide  of  the  metal.  This  property  of  sulphuric  acid  by 
which  its  hydrogen  can  be  replaced  by  a  metal  is  a  property 
that  is  common  to  all  acids.  Many  of  the  compounds  so 
formed  resemble  common  salt  in  appearance,  and  for  that 
reason,  it  has  become  customary  to  call  all  such  compounds 
salts.  Copperas,  blue  vitriol,  washing  soda,  Epsom  salts, 
alum,  and  table  salt  are  all  common  substances  which  the 
chemist  places  in  the  large  class  of  compounds  known  as 
salts.  They  are  all  formed  by  replacing  the  hydrogen  of  some 
acid  with  a  metal. 

67.  Multiple  Proportions.  It  has  been  shown  that  sul- 
phur forms  two  distinct  compounds  with  oxygen.  Each 
of  these  compounds  is  constant  in  composition  in  accord 
with  the  law  of  definite  proportions  (34).  Hydrogen  and 
oxygen  likewise  form  two  distinct  compounds,  water  and 
hydrogen  peroxide.  In  the  latter  one  part  of  hydrogen  is 
combined  with  sixteen  parts  of  oxygen,  while  in  water  one 


88  INORGANIC  CHEMISTRY 

part  of  hydrogen  is  combined  with  eight  parts  of  oxygen. 
The  ratio  between  the  amounts  of  oxygen  in  these  compounds 
when  stated  in  its  simplest  form  is  as  1  to  2. 

In  sulphur  dioxide  one  part  of  sulphur  is  united  to  one 
part  of  oxygen,  while  sulphur  trioxide  is  composed  of  one  part 
of  sulphur  to  one  and  one  half  parts  of  oxygen.  The  ratio 
of  the  oxygen  jn  these  compounds  when  expressed  in  the 
simplest  terms  is  as  2  to  3. 

A  study  of  all  the  cases  where  two  elements  unite  in  more 
than  one  proportion  has  shown  that  similar  simple  ratios 
always  exist  between  the  different  amounts  of  one  of  the 
elements  which  unite  with  a  fixed  amount  of  the  other ;  that 
is,  the  ratio  can  always  be  expressed  by  small  whole  numbers 
such  as  1,  2,  3,  4,  or  5.  This  fact  is  known  as  the  law  of 
multiple  proportions. 

EXERCISES 

Ex.  47.  Examine  a  piece  of  roll  sulphur  and  state  its  most  obvious 
physical  properties.  Will  it  dissolve  in  water  ?  In  carbon  bisulphide  ? 
Heat  the  sulphur  in  a  test  tube.  What  happens  upon  heating?  Is 
sulphur  an  element  or  a  compound?  How  does  it  occur  in  nature? 
How  is  native  sulphur  purified  ? 

Ex.  48.  Dissolve  one  half  gram  of  sulphur  in  2  cubic  centimeters 
of  carbon  bisulphide.  Pour  the  liquid  into  a  small  dish  and  allow  the 
carbon  bisulphide  to  evaporate.  Describe  the  crystals  of  sulphur  which 
form. 

Ex.  49.  Fold  a  piece  of  filter  paper  as  if  to  be  placed  in  a  funnel. 
Heat  about  half  a  test  tube  of  sulphur  until  it  just  melts  and,  holding 
the  filter  by  the  three  folds,  pour  the  melted  sulphur  into  it.  When 
the  crystals  begin  to  form  across  the  surface  pour  off  the  remaining 
liquid.  What  is  the  form  of  the  crystal  in  this  case?  Allow  the 
crystals  to  remain  undisturbed  for  a  few  days  and  examine  again. 
Has  any  change  taken  place? 

Ex.  50.    Heat  another  portion  of  sulphur  to  the  boiling  point  and 


SULPHUR  89 

pour  in  a  thin  stream  into  cold  water,  moving  the  test  tube  so  as  to 
form  a  coil  rather  than  a  solid  mass.  Describe  the  result.  Is  this 
sulphur  crystalline?  Define  amorphous.  Preserve  the  sample  and 
note  what  change  takes  place  in  a  day  or  two.  Is  this  form  of  sulphur 
stable?  What  is  the  stable  form  of  sulphur?  What  is  meant  by 
allotropic  forms  of  sulphur?  What  is  the  property  of  an  element  by 
which  it  can  exist  in  different  forms  ? 

Ex.  51.  Rub  together  four  grams  of  powdered  sulphur  and  seven 
grams  of  fine  iron  filings.  Pass  a  magnet  over  a  small  portion  of  the 
mixture.  Treat  another  small  portion  with  carbon  bisulphide,  pour 
off  the  liquid,  and  evaporate.  Have  you  a  compound  of  iron  and 
sulphur  or  a  mechanical  mixture?  Place  another  portion  in  an  old 
test  tube  and  heat  over  the  Bunsen  burner.  What  happens  ?  When 
cold,  break  the  tube  and  test  the  contents  with  the  magnet  and  with 
carbon  bisulphide.  What  results  do  you  get  ?  Has  a  chemical  change 
taken  place?  What  is  the  new  compound  called?  Are  compounds 
of  sulphur  of  frequent  occurrence?  Name  some  substances  contain- 
ing sulphur.  How  does  sulphur  resemble  oxygen  in  chemical  be- 
havior ?  What  are  the  compounds  of  sulphur  with  the  metals  called  ? 
What  makes  the  silver  spoon  turn  black  when  used  with  eggs  ?  Why 
does  a  silver  coin  become  black  when  kept  in  the  pocket  with  a  rubber 
band  ?  Silver  jewelry  sometimes  turns  black ;  where  does  the  sulphur 
come  from  ? 

Ex.  52.  Burn  a  small  quantity  of  sulphur  in  a  bottle  of  air  (or 
oxygen  if  at  hand).  Smell  the  gas  cautiously.  What  is  this  gas 
called  and  of  what  is  it  composed?  Heat  a  piece  of  iron  sulphide, 
lead  sulphide,  or  copper  sulphide  in  the  Bunsen  flame.  What  odor 
do  you  note  ?  What  is  the  source  of  the  sulphur  ?  Give  the  physical 
properties  of  sulphur  dioxide.  Place  some  flowers  and  some  pieces 
of  moist  colored  cloth  in  the  bottle  of  sulphur  dioxide.  What  happens  ? 
What  use  is  made  of  this  property  of  sulphur  dioxide  ?  How  is  sulphur 
dioxide  used  as  a  disinfectant?  Should  sulphur  dioxide  be  used  to 
preserve  fruits  and  vegetables?  What  effect  does  sulphur  dioxide 
have  upon  vegetation  ? 

Ex.  53.  (By  the  Teacher.)  Perform  the  experiment  described  in 
paragraph  64.  If  a  cylinder  of  commercial  sulphur  dioxide  is  not  at 
hand,  the  gas  may  be  generated  by  the  action  of  sulphuric  acid  on 
sodium  sulphite.  (Convince  the  class  that  this  gas  is  the  same  as 


90  INORGANIC  CHEMISTRY 

that  obtained  by  burning  sulphur.)  What  is  the  product  obtained 
in  this  experiment?  How  does  the  proportion  of  oxygen  in  this  com- 
pound compare  with  that  found  in  sulphur  dioxide?  What  are  the 
properties  of  sulphur  trioxide?  Why  was  the  platinum  used  in  this 
experiment?  What  is  meant  by  a  catalyzer?  What  other  example 
have  you  had  of  a  catalytic  agent? 

Ex.  54.  What  compound  is  formed  when  sulphur  trioxide  unites 
with  water?  Examine  the  sulphuric  acid  of  the  laboratory  and  state 
the  physical  properties.  Pour  ten  cubic  centimeters  of  sulphuric 
acid  slowly  into  twice  as  much  water.  What  happens?  Should  the 
water  ever  be  poured  into  the  acid?  Why?  What  happens  when 
sulphuric  acid  stands  exposed  to  the  air?  If  moist  air  or  other  gas 
were  forced  through  sulphuric  acid,  would  it  come  out  drier  or  more 
moist  than  before?  Put  a  few  drops  of  the  acid  on  a  clean  piece  of 
wood.  What  happens?  Dip  a  bit  of  cotton  cloth,  a  leaf  of  a  plant, 
and  a  feather  in  strong  sulphuric  acid  and  describe  the  result.  What 
is  the  cause  of  these  changes?  What  would  be  the  effect  of  spilling 
sulphuric  acid  on  your  flesh?  On  your  clothing?  Tell  something 
of  the  importance  of  sulphuric  acid.  What  is  a  common  name  for  it? 
What  is  meant  by  the  contact  method  of  making  this  acid  ? 

Ex.  55.  Put  eight  or  ten  drops  of  sulphuric  acid  in  a  tumblerful  of 
water.  Taste  it  cautiously  by  dipping  in  a  glass  rod  and  touching 
it  to  the  tongue.  How  does  the  mixture  taste?  Dip  a  piece  of  blue 
litmus  paper  into  the  liquid.  What  change  takes  place?  Of  what 
group  of  compounds  are  the  sour  taste  and  this  effect  on  litmus  paper 
characteristic  ? 

Ex.  56.  Perform  the  experiment  described  in  paragraph  66.  What 
is  the  appearance  of  the  residue  left  after  evaporation?  Of  what  is 
the  material  composed?  What  is  it  called?  What  would  be  formed 
if  iron  were  used  in  place  of  zinc?  Give  a  general  definition  for  sul- 
phates. What  does  the  chemist  mean  by  a  "salt"?  How  are  all 
salts  formed? 


CHAPTER  VIII 

THE   ATOMIC   THEORY 

4 

68.  THE  modern  science  of  chemistry  was  preceded  by 
the  work  of  the  alchemists  during  the  Middle  Ages.  These 
men  were  striving  to  find  a  method  by  which  the  common 
metals  could  be  converted  into  gold,  and  while  they  failed 
in  the  particular  thing  they  desired,  they  discovered  many 
substances  which  have  been  of  great  value  to  mankind. 
Sulphuric  acid,  nitric  acid,  and  hydrochloric  acid,  as  well 
as  certain  of  the  methods  of  extracting  metals  from  their 
ores,  are  discoveries  which  were  due  to  the  work  of  the  al- 
chemists. But  the  methods  of  these  men  were  haphazard, 
and  it  was  not  until  the  eighteenth  century,  when  the  use  of 
the  balance  made  quantitative  studies  possible,  that  the 
science  now  known  as  chemistry  had  its  beginning.  It 
was  during  this  period  that  the  law  of  definite  proportions 
(34)  and  the  law  of  multiple  proportions  (67)  were  discov- 
ered. These  laws,  it  should  be  understood,  are  merely  con- 
cise statements  of  truths  that  haw  been  proved  by  experiment. 

It  is  one  thing,  however,  to  know  a  general  fact,  and  quite 
another  thing  to  know  the  cause  of  the  fact.  While  it  is 
known  that  elements  combine  in  definite  and  multiple  pro- 
portions, it  does  not  necessarily  follow  that  it  is  known  why 
they  combine  according  to  these  laws.  It  is  natural  for 
man  to  desire  to  know  the  reason  for  the  truths  which  he 
discovers,  and  when  the  cause  cannot  be  determined  directly 

91 


92  •    INORGANIC  CHEMISTRY 

he  imagines  a  cause,  or  a  condition  which,  if  it  existed,  would 
lead  to  the  results  discovered.  Such  a  theoretical  explana- 
tion is  known  as  a  hypothesis. 

If,  now,  this  hypothesis  is  tested  in  every  way  that  sug- 
gests itself  and  all  facts  discovered  are  in  accordance  with  it, 
it  becomes  a  theory.  A  hypothesis  is  a  guess  in  regard 
to  the  cause  of  certain  phenomena,  while  a  theory  is  a  hy- 
pothesis which  has  been  thoroughly  tested  and  found  to  be 
fully  in  accord  with  the  known  facts. 

69.  The  Atomic  Theory.     The  explanation  of  the  laws 
of  definite  and  multiple  proportions,  now  generally  accepted, 
is    the    hypothesis    formulated    by    Dalton,    the    English 
chemist,  about  1804,  which  has  come  to  be  known  as  the' 
atomic  theory.     This  theory  assumes,  (1)  that  all   elements 
are  made  up  of  minute  independent  particles  called  atoms 
that    cannot    be    subdivided,   (2)    that   all    atoms   of    the 
same   element  have  the  same  size   and  weight,  while  the 
atoms  of  different  elements  have  different  weights,  (3)  that 
when  two  or  more  elements  unite,  the  action  consists  in 
the  union  of  a  definite  small  number  of  the  atoms  of  each 
element  to  form  a  small  particle  of  the  compound. 

70.  Molecules.     The  atom  is  the  smallest  particle  of  an 
element,  but  it  is  evident  that  the  smallest  particle  of  a  com- 
pound which  can  exist  must  contain  more  than  one  atom ; 
that  is,   it   must   contain  at   least  one  atom  of  each  ele- 
ment in  the  compound  and  may  contain  more  than  one  atom 
of  each  element.     This  smallest  particle  of  a  compound, 
which  consists  of  two  or  more  atoms,  is  called  a  molecule. 
Even  in  the  case  of  the  elements  it  is  not  possible  for  the 
atoms  to  exist  in  the  free  state,  but  these  also  combine 
into  groups  or  molecules.     There  are,  therefore,  two  kinds 
of  molecules ;  namely,  the  molecules  of  an  element  in  which 


THE  ATOMIC   THEORY  93 

all  the  atoms  are  alike,  and  the  molecules  of  a  compound 
in  which  there  are  at  least  two  different  kinds  of  atoms. 
The  molecule  of  hydrogen  is  supposed  to  contain  two  atoms 
of  hydrogen,  and  the  molecule  of  water  to  contain  two  atoms 
of  hydrogen  and  one  of  oxygen. 

71.  The  Atomic  Theory  Applied.     If  the  atomic  theory 
is  accepted,  it  is  easy  to  understand  why  elements  unite 
according  to  the  laws  of  definite  and  multiple  proportion. 
It  is  assumed  that  the  molecule  of  water  contains  one  atom 
of  oxygen.     If  any  more  oxygen  is  added  to  the  molecule, 
it  must  be  at  least  one  whole  atom,  for  the  atom  is  indivisible; 
but  the  addition  of  one  more  atom  would  exactly  double 
the  amount  of  oxygen  in  the  molecule.     The  facts  are  in 
accord   with  the   theory,   for  hydrogen  peroxide   contains 
exactly  double  the  quantity  of  oxygen  that  is  present  in 
water.     Sulphur  dioxide  is  assumed  to  contain  one  atom  of 
sulphur  and  two  atoms  of  oxygen,  and  sulphur  trioxide  to 
contain  one  atom  of  sulphur  and  three  atoms  of  oxygen. 
This  assumption  is  in  accord  with  the  fact  that  the  ratio 
of  oxygen  in  the  two  compounds  is  as  2  to  3.     It  must  not 
be  forgotten,  however,  that  the  laws  of  definite  and  multiple 
proportions  are  truths,  but  that  the  atomic  theory,  although 
it  is  a  conception  which  is  probably  true,  cannot  be  proved 
to  be  true.     All  the  facts  of  chemistry  discovered  since 
the  time  of  Dalton,  however,  are  in  perfect  accord  with 
the  theory,  and  by  means  of  this  theory  chemists  were  able 
to  predict  many  of  the  facts  which  have  since  been  discovered . 
At  the  present  time  the  existence  of  molecules  and  atoms 
can  scarcely  be  doubted. 

72.  Atomic  Weights.     Atoms  are  too  small  to  be  weighed 
directly,  but  if  the  atoms  of  each  element  are  all  alike  and 
of  the  same  weight,  it  ought  to  be  possible  to  assign  some 


94  INORGANIC  CHEMISTRY 

number  to  the  elements  which  would  represent  the  relative 
weights  of  the  atoms.  This  was  first  done  by  giving  to  hydro- 
gen, which  was  the  lightest  atom,  the  relative  weight  of  one, 
and  studying  the  combinations  which  the  other  elements 
made  with  it,  or  with  some  other  element  whose  relation 
to  hydrogen  had  already  been  established.  Most  of  the 
atomic  weights  have  been  determined  by  studying  the  com- 
binations of  the  various  elements  with  oxygen,  which  had 
been  determined  to  be  16 ;  that  is,  the  atom  of  oxygen  was 
said  to  be  16  times  as  heavy  as  the  atom  of  hydrogen.  As 
a  matter  of  fact  the  atomic  weights  are  now  all  based  on  the 
assumption  that  oxygen  is  16,  for  it  has  been  found  that 
there  was  a  slight  error  in  the  earlier  calculations  and  that 
hydrogen  is  1.008  if  oxygen  is  16. 

73.  Chemical  Symbols.  In  order  to  avoid  the  incon- 
venience of  using  long  names  the  chemist  represents  the 
different  elements  by  symbols.  These  symbols  consist  of 
the  first  letter  of  the  name,  unless  there  is  more  than  one 
element  with  the  same  initial  letter.  In  that  case  the  first 
element  discovered  is  designated  by  the  initial  letter,  and 
the  others  by  the  initial  letter  with  some  other  characteristic 
letter  of  the  name;  as,  for  instance,  C  is  the  symbol  for 
carbon,  but  Cl  for  chlorine  and  Ca  for  calcium.  Chemical 
symbols  are  the  same  the  world  over,  hence  where  the  initial 
letter  of  the  name  differs  in  different  languages  an  abbrevia- 
tion of  the  old  Latin  name  is  used  for  the  symbol.  Fe 
(ferrum)  is  the  symbol  for  iron,  and  Cu  (cuprum)  for 
copper. 

The  symbol  designates  not  merely  the  element,  but  stands 
in  each  case  for  one  atom  of  the  element.  Thus,  H  repre- 
sents one  atom  of  hydrogen,  O  one  atom  of  oxygen,  S  one 
atom  of  sulphur.  But  the  symbols  mean  even  more  than 


THE  ATOMIC  THEORY 


95 


this,  for  they  express  the  atomic  weights  as  well.  Thus,  0 
not  only  means  one  atom  of  oxygen,  but  also  means  that  this 
atom  weighs  sixteen  times  more  than  one  atom  of  hydrogen. 
The  table  on  the  inside  of  the  back  cover  gives  a  list  of  the 
elements,  with  their  symbols  and  atomic  weights.  A  few  of 
the  more  common  elements,  with  their  atomic  weights  stated 
in  round  numbers,  are  given  in  the  following  table : 


ELEMENT 

SYMBOL 

ATOMIC  WEIGHT 

Hydrogen    

H 

1 

Oxvffen 

o 

16 

N 

14. 

s 

32. 

Carbon    

c 

12. 

Calcium  

Ca 

40. 

Iron    

Fe  (Ferrum) 

56. 

Sodium         

Na  (Natrium) 

23. 

Chlorine 

Cl 

35.5 

Phosphorus       

P 

31. 

1C  (Kalium) 

39 

Copper 

Cu  (Cuprum) 

63  6 

Zinc 

Zn 

654 

If  more  than  one  atom  is  to  be  designated  the  proper 
numeral  is  placed  before  the  symbol,  thus : 

2  H  means  2  atoms  of  hydrogen. 

3  S  means  3  atoms  of  sulphur. 

But  if  the  atoms  are  combined  with  others  in  a  compound  a 
small  numeral  is  placed  after  and  below  the  symbol,  thus : 

H2  means  2  atoms  of  hydrogen  in  combination. 
83  means  3  atoms  of  sulphur  in  combination. 


96  INORGANIC  CHEMISTRY 


EXERCISES 

Ex.  57,  State  the  law  of  the  conservation  of  matter.  Is  the  amount 
of  matter  in  the  universe  constant  ?  Does  any  matter  disappear  when 
coal  burns  in  the  stove?  Is  the  amount  of  each  chemical  element  in 
the  universe  always  constant?  What  is  the  law  of  definite  propor- 
tions? Of  multiple  proportions?  What  is  meant  by  a  hypothesis? 
A  theory? 

Ex.  58.  State  the  atomic  theory.  Show  how  the  atomic  theory 
explains  the  law  of  multiple  proportions.  What  name  is  given  to  the 
smallest  amount  of  a  compound  which  can  exist  ?  Are  there  molecules 
of  the  elements  as  well  as  of  the  compounds?  What  is  meant  by  the 
atomic  weight  of  an  element?  By  a  chemical  symbol?  Of  what 
does  the  chemical  symbol  consist?  Just  what  does  the  symbol  for  an 
element,  S  for  example,  designate? 


CHAPTER  IX 
FORMULAS  AND  EQUATIONS 

74.  Chemical  Formulas.  A  formula  is  a  group  of  sym- 
bols that  is  used  to  express  the  composition  of  a  molecule 
of  a  compound.  Tfye  symbols  of  the  different  elements 
are  written  side  by  side,  with  the  proper  subscript  numerals 
representing  the  number  of  atoms  of  each  element.  Thus, 
H2O  is  the  formula  for  water,  and  indicates  that  a  molecule 
of  water  is  composed  of  two  atoms  of  hydrogen  and  one  of 
oxygen.  It  also  indicates  that  water  is  composed  of  2  parts 
by  weight  of  hydrogen  and  16  parts  by  weight  of  oxygen. 
Sulphur  dioxide  is  written  S02,  and  the  trioxide  SOs.  As 
the  atomic  weight  of  sulphur  is  32,  it  is  seen  that  the  dioxide 
consists  of  32  parts  by  weight  of  sulphur  to  32  of  oxygen. 
The  ratio  in  the  trioxide  is  32  of  sulphur  to  48  of  oxygen. 
The  formula  also  shows  why  one  is  called  di-oxide  and  the 
other  tri-oxide.  The  formula  for  sulphuric  acid  is  H^SO^ 
showing  that  the  molecule  contains  2  atoms  of  hydrogen,  1 
of  sulphur,  and  4  of  oxygen,  the  relative  weights  being  as 
2  to  32  to  64.  The  sum  of  the  atomic  weights  in  a  molecule 
is  the  molecular  weight.  The  molecular  weight  of  sulphuric 
acid  is  98. 

A  numeral  placed  in  front  of  a  formula  multiplies  the  mole- 
cule and  consequently  all  the  atoms  within  the  molecule. 
Thus,  3  H2SO4  represents  three  molecules  of  sulphuric  acid 
and  is  equivalent  to  6  atoms  of  hydrogen,  3  of  sulphur,  and 
12  of  oxygen.  In  certain  cases  a  group  of  elements  which 

EV.    CHEM. 7  97 


98  INORGANIC  CHEMISTRY 

act  together  are  inclosed  in  a  parenthesis  and  the  group 
may  be  multiplied  by  using  the  subscript  to  the  right  of  the 
parenthesis ;  thus,  in  Fe2  (804)3  the  group  SC>4  is  multiplied  by 
3.  If  a  numeral  is  placed  before  this  formula,  as  2  Fe2(SO4)3, 
it  means  that  the  whole  formula  is  multiplied  by  2,  and 
that  consequently  there  are  six  SC>4  groups  present  and  four 
atoms  of  iron. 

75.  Reactions.    A  chemical  reaction  is  a  special  or  limited 
chemical  change.     When  sulphuric  acid  acts  on  zinc  to  pro- 
duce hydrogen  the  change  which  takes  place  is  a  chemical  reac- 
tion.    The  burning  of  sulphur  to  produce  SO2,  the  uniting  of 
oxygen  and  copper  to  form  copper  oxide,  the  decomposition 
of  water  by  means  of  heated  iron,  are  all  chemical  reactions. 

76.  Reagents.    A  reagent  is  a  substance  capable  of  pro- 
ducing a  reaction  with  another  substance.     The  name  is 
sometimes  confined  to  those  chemicals  which  are  employed 
to  detect  the  presence  of  other  substances. 

77.  Chemical  Equations.     To  express  the  various  facts 
about  chemical  reactions  it  is  customary  to  use  a  sort  of 
chemical  shorthand  known  as  a  chemical  equation.    The  for- 
mulas representing  the  substances  which  enter   into   the 
reaction  are  connected  by  the  plus  (+)  sign  and  form  the  left- 
hand  member  of  the  equation.     The  formulas  for  the  prod- 
ucts of  the  reaction  are  placed  at  the  right,  and  the  equation 
is  read  from  left  to  right.     In  place  of  the  sign  of  equality 
as  used  in  mathematical  equations  it  is  now  customary  to 
use  the  arrow  to  connect  the  two  members  of  the  equation. 
For  example,  it  is  known  that  when  water  vapor  is  passed 
over  heated  zinc  the  result  is  the  production  of  zinc  oxide 
and  hydrogen  (21).     This  fact  may  be  represented  by  the 
following  equation : 

H20  +  Zn  -»-  ZnO  +  2  H. 


FORMULAS  AND  EQUATIONS  99 

The  equation  should  not  be  read  like  an  equation  in  mathe- 
matics, nor  should  it  be  considered  as  any  more  than  a 
brief  way  of  stating  certain  known  facts.  The  plus  sign 
should  be  read  "  and  "  and  the  arrow  translated  as  "  yields  " 
or  "  produces."  The  above  equation,  then,  means  that 
water  and  zinc  act  upon  each  other  to  produce  zinc  oxide  and 
hydrogen.  It  also  shows  that  one  molecule  of  water  reacts 
with  one  atom  of  zinc  and  produces  one  molecule  of  zinc  oxide 
and  two  atoms  of  hydrogen. 

78.  Writing  Reactions.  If  it  is  remembered  that  the 
equation  is  merely  a  brief  way  of  expressing  certain  facts, 
it  will  be  understood  that  a  complete  knowledge  of  the  reac- 
tion is  necessary  before  the  equation  can  be  written.  The  equa- 
tion cannot  be  figured  out  mathematically,  nor  can  the  equa- 
tion for  one  element  be  "  guessed  out  "  by  knowing  what 
another  will  do  under  the  same  circumstances.  When  copper 
burns  in  oxygen,  the  equation  is 

Cu  +  O  ->-  CuO. 
But  when  iron  burns  the  equation  is  as  follows  : 


In  the  case  of  phosphorus  it  is 


The  reaction  for  the  formation  of  water  may  be  expressed 
as*  follows: 


The  preparation  of  oxygen  is  represented  by  the  following 
equation  :  KC1Q3  ^  KQ  +  3  Q 

This  equation  should  be  read  :  Potassium  chlorate  yields 
potassium  chloride  and  oxygen.  The  manganese  dioxide 
is  not  written  into  the  equation  because  it  remains  unchanged 


100  INORGANIC   CHEMISTRY 

and  probably  acts  as  a  catalyzer.     The  following  equations 
will  express  the  reactions  mentioned  in  the  last  chapter. 
Formation  of  sulphides  : 


Cu  +  S  ^  CuS. 
Burning  of  sulphur  or  a  sulphide  : 


CuS  +  3  O  ->-  CuO  +  SO2. 
When  sulphur  dioxide  changes  to  trioxide  : 
SO2  +  O  ->-  SO3. 

The  platinum  is  not  written  into  the  equation  because  it 
acts  as  a  catalyzer  and  takes  no  actual  part  in  the  reaction. 
When  sulphuric  acid  is  formed,  the  equation  is 

H2O->H2SO4, 


and  when  sulphuric  acid  and  zinc  are  used  to  prepare  hy- 
drogen, _ 


This  equation  should  be  read  :  zinc  and  sulphuric  acid  yield 
zinc  sulphate  and  hydrogen. 

Since  the  atoms  are  indestructible,  it  follows  that  the 
same  number  of  atoms  of  each  element  should  be  found  on 
both  sides  of  the  arrow.  The  equations  are  also  quantita- 
tive expressions.  The  last  equation  expresses  the  fact  that 
65.4  parts  by  weight  of  zinc  will  .react  writh  98  parts  of  sul- 
phuric acid  and  produce  161.4  parts  of  zinc  sulphate  and  2 
parts  of  hydrogen. 

Thus  if  the  quantity  of  any  one  of  the  factors  of  the  equa- 
tion is  known,  it  will  be  seen  that  any  or  all  of  the  others  can 


FORMULAS  AND  EQUATIONS  101 

be  calculated.  For  example,  suppose  the  problem  is  to  find 
how  much  sulphuric  acid  is  required  to  produce  7  pounds  of 
hydrogen.  First  write  the  equation  with  the  molecular 
weights  (73)  written  below : 

Zn  +  H2SO4  ->•  ZnSO4  +  H2, 
65.4         98          161.4         2. 

The  equation  shows  that  2  parts  of  hydrogen  can  be  produced 
from  98  parts  of  sulphuric  acid ;  this,  therefore,  establishes 
the  ratio,  and  the  problem  is  merely  a  matter  of  simple 
proportion : 

2:98  =  7:z,  x=  343. 

Consequently  343  pounds  of  sulphuric  acid  are  required  to 
produce  the  7  pounds  of  hydrogen.  To  solve  similar  prob- 
lems, first  write  the  equation  with  the  correct  atomic  or 
molecular  weights,  and  then  state  the  problem  in  the  form 
of  a  proportion,  like  the  one  given  above. 

79.  Chemical  Affinity.  It  is  not  known  why  certain 
substances  act  upon  each  other  chemically  and  others  do 
not.  The  fact  that  a  piece  of  sulphur  will  burn  when  heated 
and  platinum  will  not  is  well  known,  but  why  this  is  so  no 
one  can  tell.  For  want  of  a  better  name  this  force,  or  attrac- 
tion, is  called  chemical  affinity.  Whatever  this  force  is 
that  holds  the  elements  together,  it  is  very  important; 
for  without  it  the  compounds  could  not  exist,  and  if  it  ceased 
to  act  all  the  complex  substances  of  the  animal,  vegetable, 
and  mineral  kingdoms  would  dissociate  into  a  few  simple 
substances  known  as  elements.  Elements  that  readily 
unite  are  said  to  have  great  affinity  for  each  other.  Sulphur, 
since  it  unites  with  oxygen,  is  said  to  have  affinity  for  oxygen. 


102  INORGANIC  CHEMISTRY 

Platinum,  which  cannot  be  made  to  burn  in  air,  is  said  to 
have  slight  affinity  for  oxygen. 

80.  Valence.     The  power  that  an  atom  of  one  element 
has  to  unite  with  one  or  more  atoms  of  another  element  is 
called  its  valence.     Here,  again,  hydrogen  is  used  as  the 
standard  and  is  rated  at  1.     Any  atom  that  can  hold  one 
atom  of  hydrogen  in  combination  is  said  to  have  a  valence 
of  1,  or  to  be  univalent.     If  it  can  combine  with  2  atoms  of 
hydrogen,   it   is   bivalent.    Oxygen   is   bivalent   because   it 
unites  with  2  atoms  of  hydrogen  (H2O) .     Elements  which  do 
not  unite  with  hydrogen  are  compared  with  oxygen  or  some 
other  element  which  does  unite  with  hydrogen.     An  atom  of 
copper  unites  with  one  atom  of  oxygen  and  consequently 
must  be  bivalent.     The  zinc  atom  does  not  unite  with  hydro- 
gen, but  since  it  replaces  the  2  atoms  of  hydrogen  in  sul- 
phuric acid,  it  is  bivalent.     The  matter  of  valence  would 
be  very  simple  if  all  elements  had  just  one  valence,  but  some 
of  them  vary  in  valence.     Sulphur  is  apparently  quadri- 
valent in  SO2  and  hexavalent  in  SOs.     When  an  element 
exhibits  more  than  one  valence,  it  is  generally  true  that 
the  compounds  at  one  of  the  valences  are  much  more  stable. 
The  compounds  in  which  sulphur  has  a  valence  of  six  are 
much  more  stable  than  those  in  which  it  appears  to  have  a 
valence  of  four. 

81.  Hydrogen   Peroxide.      The    stable    combination    of 
hydrogen  and  oxygen  is  water,   H2O,   sometimes   written 
H — 0 — H.     In  hydrogen  peroxide  another  atom  of  oxygen 
is  introduced  into  the  molecule,  making  it  H— O — O — H 
or  H2O2.     This  oxide  of  hydrogen  readily  changes  to  the 
more  stable  compound  v/ater,  and  one  atom  of  oxygen  is 
liberated.     For  this   reason,   hydrogen   peroxide,    or   more 
properly  dioxide,  is  a  strong  oxidizing  agent.     It  gradually 


FORMULAS  AND  EQUATIONS  103 

decomposes  into  water  and  oxygen  upon  standing,  but  does 
so  very  quickly  if  in  contact  with  a  substance  that  can  be 
oxidized.  The  equation  is 


82.  Physics  and  Chemistry.  From  what  has  been  said 
in  this  chapter  it  must  be  evident  that  so  long  as  the  molecule 
remains  intact  the  chemical  composition  of  a  substance  does 
not  change.  If  the  make-up  of  the  molecule  changes,  new 
substances  are  formed,  and  the  change  which  takes  place 
is  a  chemical  change.  It  may  be  said,  then,  that  physical 
changes  are  those  in  -which  the  composition  of  the  molecule 
is  not  affected,  while  in  chemical  changes  the  atoms  are 
rearranged  into  new  and  different  molecules. 

EXERCISES 

Ex.  59.  What  is  a  chemical  formula  and  what  does  it  represent? 
What  is  the  formula  for  sulphuric  acid  ?  What  facts  about  sulphuric 
acid  are  represented  by  this  formula  ?  What  is  meant  by  the  molec- 
ular weight  of  a  compound?  The  formula  for  potassium  chlorate  is 
KC1O3;  what  is  its  molecular  weight?  What  percentage  of  oxygen 
does  it  contain? 

Ex.  60.  What  is  meant  by  a  chemical  equation  ?  Of  what  use  are 
these  equations?  How  should  they  be  read?  What  must  be  known 
in  order  to  write  an  equation  ?  How  much  potassium  chlorate  would 
be  needed  to  produce  100  pounds  of  oxygen  ? 

What  is  meant  by  chemical  affinity?  By  valence?  The  formula 
for  carbon  dioxide  is  CO2  ;  what  is  the  valence  of  carbon  ?  What  is 
the  relation  of  the  molecule  to  chemical  and  physical  changes  ? 


CHAPTER  X 
ACIDS  OF  SULPHUR   AND   HYDROGEN   SULPHIDE 

83.  Sulphurous  Acid.  Sulphur  dioxide  dissolves  readily 
in  water,  one  volume  of  the  latter  absorbing  forty  volumes 
of  the  gas.  This  liquid  has  a  sour  taste  and  turns  blue  litmus 
paper  red,  from  which  it  may  be  inferred  that  the  solution 
contains  an  acid.  The  reaction  may  be  expressed  as  follows : 

SO2  +  H20  ->-  H2SO3. 

The  compound  H2S03  is  sulphurous  acid.  When  the  solu- 
tion is  heated,  the  acid  decomposes  into  water  and  sulphur 
dioxide,  the  latter  being  driven  off.  This  reaction  may  be 
written : 

H2SO3  ->-  H2O  +  SO2. 

The  fact  that  sulphurous  acid  decomposes  when  heated 
makes  it  impossible  to  concentrate  it  and  obtain  it  free  from 
water,  as  can  be  done  with  sulphuric  acid,  which  does  not 
completely  decompose  upon  boiling.  Sulphurous  acid  pos- 
sesses marked  bleaching  properties.  In  fact  the  bleaching 
and  disinfecting  properties  which  were  referred  to  in  de- 
scribing sulphur  dioxide  should  properly  be  ascribed  to  sul- 
phurous acid,  for  it  was  noted  that  these  effects  were  produced 
when  the  substance  acted  upon  was  moist.  Under  these 
circumstances  the  sulphur  dioxide  unites  with  the  moisture 
to  form  sulphurous  acid. 

104 


ACIDS  O7  SULPHUR  105 

Sulphurous  acid  can  readily  be  oxidized  to  sulphuric  acid  : 
H2SO3  +  O  ->•  H2SO4. 

This  change  is  brought  about  to  a  limited  extent  by  the 
oxygen  of  the  air  uniting  with  the  sulphurous  acid.  The 
change  can  also  be  effected  by  means  of  oxidizing  agents, 
as,  for  instance,  hydrogen  peroxide  : 

H2SO3  +  H2O2  ->-  H2SO4  +  H2O. 

This  property  of  readily  taking  on  oxygen  makes  sulphurous 
acid  a  strong  reducing  agent. 

84.  Sulphuric  Acid  by  Chamber  Process.  The  older 
method  of  preparing  sulphuric  acid,  known  as  the  chamber 
process,  depended  upon  the  oxidation  of  sulphurous  acid 
by  means  of  one  of  the  oxides  of  nitrogen.  Under  certain 
circumstances  this  compound  will  give  up  a  part  of  its 
oxygen,  and  later  will  take  up  again  a  like  quantity  of  oxygen 
from  the  air.  This  oxide  may  be  represented  by  the  formula 
NO2.  In  manufacturing  sulphuric  acid,  sulphur  or  pyrites  is 
burned  to  produce  S02,  and  this  compound  and  steam  are 
conducted  into  lead-lined  chambers.  The  lead  lining  is 
used  because  sulphuric  acid  has  very  little  effect  on  lead. 
The  sulphur  dioxide  and  steam  unite  to  form  sulphurous 
acid.  The  NO2  gas  which  is  obtained  from  nitric  acid  then 
acts  upon  the  sulphurous  acid  : 

H2SO3  +  N02  ->-  H2S04  +  NO. 

Air  is  also  admitted,  and  the  gas  takes  up  oxygen  and  changes 
back  to  NO,: 


Theoretically  the  same  amount  of  NO2  could  be  used  indefi- 
nitely, as  it  acts  much  like  a  catalyzer.     Practically  there  is 


106  INORGANIC  CHEMISTRY 

always  some  loss  of  the  nitrogen  oxide,  since  some  of  it  is 
dissolved  in  the  sulphuric  acid  and  removed  from  the  cham- 
ber with  it.  The  actual  chemical  changes  which  take  place 
in  the  chamber  are  much  more  complicated  than  are  indi- 
cated in  the  foregoing  equations,  and  are  not  fully  under- 
stood, but  the  essential  feature  of  the  processes  this  power 
of  the  oxide  of  nitrogen  to  take  an  intermediate  part  in  the 
reaction  between  sulphurous  acid  and  the  oxygen  of  the 
air,  or,  as  it  is  often  expressed,  to  act  as  a  carrier  of  oxygen. 
This  process  results  in  sulphuric  acid  of  50  to  60  per  cent 
strength  and  with  some  impurities,  namely,  lead  and  nitro- 
gen compounds.  Where  pure  acid  is  required  the  contact 
method  is  generally  used.  The  chamber  method  is  used 
by  many  of  the  fertilizer  factories  as  the  so-called  chamber 
acid  is  about  the  strength  needed  in  the  making  of  fertilizers, 
and  the  little  impurity  found  in  the  acid  is  of  no  moment. 
Fully  one  half  of  all  the  sulphuric  acid  produced  in  the  world 
is  used  in  the  manufacture  of  fertilizers. 

85.  Two  Acids  of  Sulphur.  It  will  be  noticed  that  there 
are  two  acids  containing  hydrogen,  sulphur,  and  oxygen, 
the  difference  in  the  formulas  being  one  atom  of  oxygen. 
These  acids  are  H2SO3  and  H2SO4.  Some  other  elements 
also  form  more  than  one  acid  in  which  the  molecules  differ 
only  in  the  amount  of  oxygen  present.  To  distinguish  be- 
tween these  acids  it  is  customary  to  use  the  ending  "  ous  " 
for  the  acid  having  the  smaller  amount  of  oxygen,  and  the 
ending  "  ic"  for  the  acid  with  the  larger  amount,  hence, 
sulphurous  acid  for  H^SOs  and  sulphuric  acid  for  H2SO4. 
In  studying  sulphuric  acid,  it  was  found  that  the  hydrogen 
of  the  acid  could  be  replaced  by  a  metal  to  form  a  saltlike 
substance.  The  same  thing  holds  true  of  sulphurous  acid 
in  a  more  limited  way.  The  best-known  compound  of  this 


ACIDS  OF  SULPHUR  107 

class  is  sodium  sulphite,  which  is  commonly  used  in  pho- 
tography. It  has  the  formula  Na^SOs.  The  sodium  atom 
is  univalent,  hence  two  atoms  are  required  to  replace  the 
two  hydrogen  atoms  of  sulphurous  acid.  The  sulphites, 
like  sulphurous  acid,  are  strong  reducing  agents.  They 
take  on  oxygen  and  change  to  sulphates,  thus  : 


This  change  takes  place  slowly  when  the  salt  is  exposed  to 
the  air,  and  consequently  nearly  all  samples  of  sulphites 
contain  some  sulphates  unless  carefully  protected.  The 
salt  of  an  acid  ending  in  "  ous  "  has  the  suffix  ite;  the  salt 
of  an  acid  ending  in."  ic  "  has  the  suffix  ate;  hence,  the  terms 
sulphite  and  sulphate. 

86.  Sulphuric  Acid  Used  to  Prepare  Other  Acids.  When 
sulphuric  acid  is  added  to  the  salts  of  other  acids,  the  metal 
of  the  salt  and  the  hydrogen  of  the  sulphuric  acid  change 
places,  and  a  sulphate  and  the  acid  of  the  original  salt  are 
formed.  If  sulphuric  acid  is  added  to  sodium  sulphite,  this 
reaction  takes  place  : 

Na^SOs  +  H2SO4  -»-  NasSO,  +  H2SO3. 

As  sulphurous  acid  happens  to  be  a  very  unstable  acid  and 
is  readily  decomposed  into  sulphur  dioxide  and  water,  the 
equation  is  generally  written  to  express  that  fact  ;  thus, 

Na2SO3  +  H2SO4  ->-  NasSO,  +  H2O  +  SO2. 

The  method  used  for  the  preparation  of  sulphurous  acid 
is  of  general  application,  and  many  of  the  well-known  acids 
are  prepared  by  the  action  of  sulphuric  acid  on  the  salt  of 
the  desired  acid.  This  method  will  be  used  repeatedly  in 
the  laboratory. 


108  INORGANIC  CHEMISTRY 

87.  Hydrogen  Sulphide.  If  dilute  sulphuric  acid  is 
added  to  a  sulphide,  like  one  of  the  sulphides  of  iron,  a  gas 
is  given  off  which  is  colorless,  but  which  has  a  very  offensive 
odor  suggestive  of  rotten  eggs.  This  gas,  which  has  the 
formula  H2S,  has  been  named  hydrogen  sulphide  although 
it  is  popularly  known  as  sulphureted  hydrogen.  The  fol- 
lowing equation  represents  its  formation : 

FeS  +  H2S04  ^  FeSO4  +  H2S. 

This  gas  exists  naturally  in  sulphur  springs,  and  in  the 
air  in  the  vicinity  of  volcanoes.  It  is  poisonous  and  even 
in  small  quantities  causes  headache  and  nausea.  It  is 
slightly  soluble  in  water,  and  the  solution  is  frequently  used 
in  the  analytical  laboratory.  This  solution  turns  blue  litmus 
paper  red  and  in  other  ways  gives  evidence  of  being  an  acid ; 
it  is,  therefore,  often  called  hydrosulphuric  acid.  Here, 
then,  is  an  acid  which  contains  no  oxygen,  from  which  fact 
it  may  be  inferred  that  Lavoisier  was  mistaken  in  his  idea 
that  oxygen  is  found  in  all  acids.  It  will  be  seen  later 
that  there  are  other  acids  which  contain  no  oxygen,  one  of 
them,  hydrochloric  acid,  being  commercially  very  important. 
Hydrogen  sulphide  is  often  formed  during  the  decay  of 
organic  matter  containing  sulphur,  especially  of  eggs  and 
other  animal  matter.  As  most  metallic  sulphides  are  insol- 
uble, hydrogen  sulphide  added  to  a  solution  of  a  salt  of  the 
metal  will  cause  a  precipitation  of  the  insoluble  sulphide. 
When  H2S  is  added  to  copper  sulphate,  the  following  reac- 
tion takes  place : 

CuSO4  +  H2S  ->-  CuS  +  H2SO4. 

The  copper  sulphide,  being  insoluble,  is  precipitated.  A  piece 
of  paper  which  has  been  moistened  with  a  solution  of  a  lead 
salt,  such  as  lead  acetate  (sugar  of  lead),  turns  black  if 


HYDROGEN   SULPHIDE  109 

exposed  to  the  hydrogen  sulphide,  owing  to  the  formation 
of  lead  sulphide.     This  is  a  test  for  hydrogen  sulphide. 

88.  Chemical  Tests.  A  chemical  test  is  a  reaction  used 
to  recognize  or  detect  the  presence  of  a  particular  element 
or  compound.  The  blackening  of  lead  acetate  paper  shows 
the  presence  of  hydrogen  sulphide.  The  test  for  hydrogen 
is  the  fact  that  it  burns  and  forms  water ;  for  oxygen,  that 
it  causes  a  glowing  splint  to  burst  into  flame.  There  is  no 
simple  test  for  nitrogen  because  it  is  so  inactive.  The  test 
for  sulphur  is  the  fact  that  SC>2  is  formed  upon  burning; 
for  a  sulphite,  that  SC>2  is  given  off  when  a  strong  acid  is 
added  to  it;  for  sulphuric  acid  or  a  sulphate,  that  a  white 
precipitate,  which  will  not  dissolve  in  hydrochloric  acid, 
is  formed  when  a  solution  of  barium  chloride  is  added. 
Other  tests  will  be  discussed  later. 

EXERCISES 

Ex.  61.  Place  about  two  ounces  of  water  in  a  wide-mouth  bottle 
and  shake  the  bottle  so  as  to  moisten  its  sides.  By  means  of  the 
crayon  cup  (Fig.  56)  burn  a  small  quantity  of  sulphur  in  the  bottle, 
keeping  the  mouth  covered.  When  the  sulphur  has  stopped  burning, 
remove  the  crayon  cup  and  shake  the  bottle  vigorously.  Have  you 
any  evidence  that  the  sulphur  dioxide  has  dissolved  in  the  water? 
Taste  a  drop  of  the  liquid.  Test  it  with  blue  litmus  paper.  What  are 
the  results  ?  Does  the  liquid  contain  an  acid  ?  Write  the  equation  for 
the  formation  of  the  acid.  Heat  a  few  drops  of  the  liquid  in  .a  test 
tube.  Is  SO2  given  off  ?  Write  the  reaction.  Can  sulphurous  acid 
be  prepared  in  concentrated  form?  Why?  Dip  a  piece  of  colored 
calico  in  the  liquid  and  note  the  effect.  Will  dry  SO2  bleach  ?  What 
conditions  are  necessary  to  bleach  with  burning  sulphur? 

Ex.  62.  Add  a  few  drops  of  sulphuric  acid  to  a  little  water  in  a  test 
tube.  Now  add  a  few  drops  of  the  laboratory  solution  of  barium 
chloride.  A  white  precipitate  which  will  not  dissolve  in  hydrochloric 
acid  forms  immediately.  This  is  a  test  for  sulphuric  acid.  To  a  little 


110 


INORGANIC  CHEMISTRY 


of  the  solution  of  sulphurous  acid  add  the  barium  chloride  solution. 
No  precipitate  will  form.  To  another  portion  of  sulphurous  acid  add 
a  few  drops  of  hydrogen  peroxide  and  then  add  barium  chloride.  Have 
you  any  proof  that  sulphuric  acid  has  been  formed?  Write  the  re- 
action. What  is  the  principle  upon  which  the  chamber  method  of 
making  sulphuric  acid  depends?  What  is  the  purpose  of  the  oxide  of 
nitrogen?  Why  is  it  called  a  carrier  of  oxygen?  Is  the  acid  made 
by  the  chamber  process  pure?  What  is  the  strength  of  chamber 
acid  ?  Is  much  sulphuric  acid  used  in  the  manufacture  of  fertilizers  ? 

Ex.  63.  Give  the  formulas  for  the  two  acids  of  sulphur.  When 
an  element  forms  two  acids,  how  are  they  named?  What  are  the 
salts  of  sulphurous  acid  called  ?  What  happens  to  sodium  sulphite 
upon  standing  exposed  to  the  air?  When  sulphuric  acid  is  added  to 
sodium  sulphite,  what  change  takes  place  ?  Write  the  reaction.  Is 
this  a  general  method  for  preparation  of  acids  ? 

Ex.  64.  Arrange  apparatus  as  in  Fig.  73.  Place  in  the  bottle  a 
few  pieces  of  iron  sulphide.  Through  the  thistle  tube  add  dilute 

sulphuric  acid.  Describe  the  gas  which 
is  evolved.  Write  the  reaction.  Place 
the  end  of  the  delivery  tube  in  a  bottle 
half  full  of  water  and  allow  the  gas  to 
bubble  through  for  some  time.  Test  the 
solution  with  litmus  paper.  Have  you 
any  proof  that  an  acid  is  present? 
What  is  it  called?  Does  it  contain 
any  oxygen  ?  How  is  hydrogen  sulphide 
formed  in  nature?  Where  is  it  found 
naturally  ?  To  a  solution  of  copper  sul- 
phate (blue  vitriol),  and  to  a  solution 
of  lead  acetate,  add  a  little  of  the  hy- 
drogen sulphide  solution.  What  hap- 
pens ?  Are  most  of  the  sulphides  soluble 
or  insoluble  ? 

Ex.  65.  Explain  how  you  could  test 
for  hydrogen  sulphide.  How  could  you  tell  whether  a  solid  was  a 
sulphide?  Try  the  test  with  lead  acetate  paper.  What  test  is  used 
to  detect  sulphur  ?  A  sulphite  ?  Sulphuric  acid  and  sulphates  ?  How 
can  you  tell  whether  a  gas  is  hydrogen  or  oxygen  ? 


FIG.  73.  — Apparatus  for  the  pro- 
duction of  hydrogen  sulphide. 


CHAPTER  XI 
CARBON 

CAKBON  is  an  element  known  to  everyone  in  the  form  of 
the  diamond,  graphite  or  black  lead,  charcoal,  lampblack, 
and  coal.  Like  sulphur  it  exists  in  several  allotropic  forms. 

89.  Diamond  and  Graphite.     The   diamond  is  a  brittle 
crystalline  form  of  pure  carbon.     It  is  insoluble  in  all  liquids 
and  is  the  hardest  substance  known.     If  it  is  heated  to  a 
very  high  temperature  in  such  a  way  that  air  is  excluded,  it 
swells  and  is  converted  into  a  black  mass.     Heated  to  a  high 
temperature  in  oxygen,  it  burns  completely,  yielding  only  car- 
bon dioxide. 

Graphite,  also  called  black  lead,  and  plumbago,  is  a 
soft,  shiny,  black  solid  which  is  smooth  and  soapy 
to  the  touch.  Pure  graphite  contains  nothing  but  carbon. 
It  exists  in  crystals,  but  the  crystalline  form  is  different 
from  that  of  the  diamond.  Like  the  diamond,  it  produces 
only  carbon  dioxide  when  burned.  It  is  used  in  the  manu- 
facture of  lead  pencils  and  stove  polish,  and  as  a  lubricant 
where  oil  cannot  well  be  used. 

90.  Wood  Charcoal.     The  diamond  and  graphite  are  the 
only  pure  crystalline  forms  of  carbon,  but  the  element  is 
known  in  many  impure  and  amorphous  forms.     One  of  the 
best  known  of  these  is  ordinary  wood  charcoal.     Wood  con- 
sists largely  of  carbon  united  with  oxygen  and  hydrogen. 
If  it  is  heated  without  access  of  air,  the  oxygen  and  hydrogen 

111 


112 


INORGANIC  CHEMISTRY 


and  part  of  the  carbon  are  driven  off  in  various  liquid  and 
gaseous  compounds,  and  the  remainder  of  the  carbon  is  left 
behind  in  the  form  of  charcoal.  It  is  almost  pure  carbon, 
the  only  impurity  being  the  small  amount  of  mineral  matter 
which  it  contains.  Charcoal  is  a  black,  brittle  substance, 
that  often  retains  the  form  of  the  wood  from  which  it  was 
made.  It  is  insoluble  in  water  or  acids,  and  burns  without 
flame  or  smoke.  It  resists  the  action  of  chemicals  and  of  de- 
cay bacteria ;  hence  fence  posts,  and  telegraph  and  telephone 
poles  are  often  charred  before  being  put  into  the  ground. 

Wood  charcoal  is  now  commonly  made  by  heating  wood 
in  closed  iron  retorts,  no  air  whatever  being  admitted.     By 

this  method  the  vola- 
tile products  can  be 
condensed  and  saved. 
Among  the  volatile 
substances  of  value 
produced  in  this  way 
are  wood  alcohol  and 
acetic  acid.  Such  a 
process  as  this  is 
known  as  destructive 
distillation. 

The  older  method  of 
making  charcoal,  and 
the  one  still  largely 
used,  is  to  construct  a 

FIG.  74. — The  exterior  and  section  of  a  char-          •,  -IP  i 

coal  furnace.  large      pile      ot      WOOd 

(Fig.  74)  so  arranged 

as  to  leave  spaces  between  the  pieces.  The  pile  is  covered 
with  sods  and  earth  to  prevent  free  access  of  air,  although 
small  holes  are  left  at  the  bottom  and  a  large  one  at  the 


CARBON  113 

top.  The  wood  is  lighted  at  the  bottom  and  the  fire  is  so 
controlled  that  it  will  smolder.  The  burning  of  the  wood 
at  the  bottom  of  the  pile  heats  the  wood  above  sufficiently 
to  drive  off  the  volatile  matter.  After  some  time  the  holes 
are  all  closed  to  smother  the  fire,  and  then  the  pile  is  un- 
covered and  the  charcoal  is  removed.  A  very  pure  form  of 
charcoal  for  use  in  medicine  is  sometimes  produced  from 
white  sugar. 

91.  Animal  charcoal  is  most  commonly  made  by  heating 
bones  in  closed  retorts.     This  form  is  also  known  as  bone 
black.     Unless  treated  with  acid  to  dissolve  the  mineral 
matter  of  the  bone  it  contains  only  about  10  per  cent  of 
carbon.     Animal  charcoal  is  produced  also  from  dried  blood, 
a  process  by  which  a  much  purer  form  of  carbon  is  obtained. 

All  these  forms  of  charcoal  have  the  power  of  absorbing 
offensive  gases  and  are,  therefore,  used  as  deodorizers. 
Charcoal  filters  are  used  to  remove  objectionable  substances 
from  water.  Charcoal  also  removes  certain  coloring  matters 
from  solutions.  This  property  of  charcoal  (especially  of 
animal  charcoal)  is  utilized  in  refining  sugar.  The  colored 
solution  obtained  from  beet  or  sugar  cane  is  passed  through 
bone-black  filters  which  remove  the  color,  making  possible 
the  production  of  a  white  sugar.  Charcoal  is  used  also  in 
the  manufacture  of  gunpowder  (207). 

92.  Coal.     The   different   varieties   of   coal,  which  were 
formed  by  the  gradual  decomposition  of  vegetable  matter  in 
an  insufficient  supply  of  air,  are  forms  of  amorphous  carbon. 
The  vegetable  origin  is  often  shown  by  the  fossil  remains  of 
leaves  and  stems  of  plants  found  in  the  coal.     All  forms  of 
coal  contain  other  substances  in  addition  to  the  carbon. 
The  different  varieties  of  coal  are  commonly  classified  as 
hard  and  soft  coals.     Hard  coal,  or  anthracite,  is  hard  and 

EV.    CHEM. — 8 


114  INORGANIC   CHEMISTRY 

lustrous.  It  is  ignited  with  difficulty  and  burns  with  little 
flame,  producing  an  intense  heat.  It  contains  about  95 
per  cent  of  carbon.  Soft,  or  bituminous,  coal  burns  with  a 
smoky  flame,  and  much  volatile  matter  is  produced,  as  can 
be  seen  by  watching  the  little  jets  of  flame  which  dart  from  a 
piece  of  burning  soft  coal.  It  contains  about  80  per  cent  of 
carbon  and,  therefore,  has  a  larger  percentage  of  other 
compounds  than  has  hard  coal. 

93.   Coke  is  made  by  heating  soft  coal  in  an  air-tight  ap- 
paratus.    Large   quantities   of   coke   are   produced   in   the 


FIG.  75.  —  Beehive  coke  ovens. 

manufacture  of  illuminating  gas.  The  bituminous  coal  is 
placed  in  large  retorts  and  heated  until  all  volatile  matter 
is  driven  off,  the  material  remaining  in  the  retort  being  coke. 
It  will  thus  be  seen  that  coke  bears  the  same  relation  to  coal 
that  charcoal  does  to  wood.  In  addition  to  gas,  referred  to 
above,  the  heating  of  soft  coal  drives  off  coal  tar,  ammonia, 
and  other  volatile  substances,  which  are  utilized  in  modern- 
coking  plants.  Many  thousand  tons  of  coke  are  made  in 
the  so-called  "  beehive  "  ovens  (Fig.  75),  where  no  attempt 
is  made  to  save  the  volatile  products.  Millions  of  dollars 
worth  of  valuable  products  are  wasted  annually  in  this  way. 


CARBON  115 

94.  Lampblack  is  a  very  finely  divided  form  of   carbon 
which  is  deposited  on  cold  objects  placed  in  the  flames  of 
burning  oils.     Oils  are  very  rich  in  carbon,  and  to  produce 
lampblack  they  are  burned  in  a  limited  supply  of  air.    When 
the  dense  smoke  arising  from  them,  which  is  mainly  finely- 
divided  carbon,  is  cooled,  the  carbon  is  deposited.     Lamp- 
black is  one  of  the  purest  forms  of  amorphous  carbon.     It 
is  used  in  making  printer's  ink  and  certain  black  paints. 

Carbon  is  found  also  in  all  organic  substances,  both  animal 
and  vegetable.  It  is  a  constituent  of  all  kinds  of  peat  and 
humus,  as  well  as  of  natural  gas,  petroleum,  and  asphalt. 
It  exists  in  limestone,  chalk,  marble,  and  all  other  carbon- 
ates. In  the  air  it  is  found  as  carbon  dioxide.  It  forms 
more  different  compounds  than  any  other  element,  and  it 
is  said  that  more  than  100,000  carbon  compounds  have 
been  prepared  and  analyzed. 

95.  Properties  of  Carbon.     Notwithstanding  their  marked 
differences  in  appearance  all  these  forms  of  carbon  have  some 
properties  in  common.     They  are  insoluble  in  all  ordinary 
liquids.     They  are  tasteless  and  odorless.     They  cannot  be 
melted.     They  can  actually  be  changed  one  into  the  other, 
for  both  graphite  and  diamonds  of  microscopic  size  have 
been    prepared    artificially    from    amorphous    carbon.     At 
ordinary  temperatures  carbon  is  inactive.     At  high  temper- 
atures all  forms  can  be  made  to  burn,  and  the  prodiict  in 
each  case  is  the  carbon  dioxide  (CO2).     Carbon  is  a  strong 
reducing  agent,  and  when  heated  with  the  oxide  of  a  metal, 
for  instance,  will  unite  with  the  oxygen,  leaving  the  metal 
free.     When  copper  oxide  is  heated  with  charcoal  the  reaction 
may  be  written  thus  : 

2  CuO  +  C  ^  2  Cu  +  CO2. 


116  INORGANIC  CHEMISTRY 

This  method  is  commonly  used  in  the  extraction  of  metals 
from  their  ores.  If  the  ore  is  an  oxide,  it  is  heated  directly 
with  carbon.  If  the  metal  is  in  the  form  of  a  sulphide  it  is 
first  roasted  to  change  it  to  the  oxide,  after  which  it  is  reduced 
by  heating  it  with  carbon.  The  chief  use  of  carbon,  however, 
is  as  a  fuel. 

96.  Flames  due  to  a  Burning  Gas.  In  Chapter  V,  com- 
bustion was  defined  as  "  the  union  of  a  substance  with 
oxygen  with  the  evolution  of  light  and  heat."  In  the  every- 
day  sense,  however,  combustion  consists  in  the  burning,  or 
oxidation,  of  a  material  containing  carbon ;  for  all  ordinary 
fuels,  whether  gaseous,  liquid,  or  solid,  contain  carbon.  A 
marked  difference  is  noticeable  in  the  manner  in  which 
the  different  fuels  burn.  Some  of  them  burn  with  a  flame 
and  some  do  not.  The  gases  all  produce  flames,  and  so  do 
the  liquid  fuels.  Of  the  solid  fuels,  wood  and  soft  coal  burn 
with  a  flame,  while  charcoal  and  coke  do  not.  Anthracite 
gives  a  very  feeble  flame.  Careful  study  of  flames  has 
shown  that  they  always  consist  of  burning  gases.  That  this 
is  true  of  a  gaseous  fuel  is  evident,  but  it  is  equally  true  of 
kerosene  or  other  burning  oils.  In  the  case  of  the  kerosene 
lamp,  for  instance,  the  gas  which  burns  is  produced  from  the 
oil  which  is  drawn  up  the  wick  by  capillary  attraction  and 
then  volatilized  by  the  heat  of  the  flame. 

In  the  case  of  the  candle  the  heat  first  melts  the  wax,  and 
the  liquid  thus  formed  is  drawn  up  the  wick  and  then  con- 
verted into  a  gas  that  burns.  That  gas  is  actually  formed 
during  the  burning  of  a  candle  can  be  shown  by  placing  the 
lower  end  of  a  piece  of  glass  tubing  in  the  center  of  the 
flame ;  the  gas  passes  up  the  tubing  and  can  be  ignited  at  the 
upper  end  A  (Fig.  76) .  Flames  are  produced  when  wood  and 
soft  coal  are  burned,  because  both  these  materials  contain 


CARBON 


117 


FIG.  76.  —  Ignition  of 
gas  from  the  inner  zone  of 
a  candle  flame. 


volatile  substances  which  are  converted  into  gases  by  the 
heat.     The  method  of  preparing  charcoal  and  coke  is  such 
that  all  these  volatile  substances  are 
driven  off.     Charcoal  and  coke,  there- 
fore,  burn  without  a  flame  because 
there  is  no  volatile  matter  present  to 
be  converted  into  a  gas.     Anthracite 
contains  very  little    volatile    matter, 
and  so  the  flaming  during  its  burning 
is  very  slight. 

97.  Luminosity  of  Flames.  There 
is  a  marked  difference  in  the  lumi- 
nosity of  flames,  the  variation  de- 
pending partly  on  the  gas  itself  and 
partly  on  the  way  in  which  it  is 

burned.  Hydrogen  burns  with  a  non-luminous  flame; 
natural  gas  gives  more  light  than  hydrogen  but  not  so  much 
as  coal  gas ;  and  acetylene  burns  with  a  more  luminous 
flame  than  either  natural  gas  or  coal 
gas.  It  has  been  found  that  when  the 
combustion  of  a  gas  is  complete  the 
flame  is  always  non-luminous.  The 
Bunsen  burner  used  in  the  laboratory 
illustrates  this  point  (Fig.  77).  It  is 
constructed  with  the  idea  of  mixing 
the  gas  and  the  air  in  such  proportions 
as  to  bring  about  the  complete  com- 
bustion of  the  gas.  The  gas  enters  at 
FIG.  77. -section  of  a  Bun-  the  base  of  the  burner  at  A  and  is 

sen  burner.  mjxed  ^^  ^  ^  entermg  at  the  side 

holes  BB,  and  the  mixture  of  gas  and  air  is  burned  at  the 
top  C.    If  the  amount  of  air  entering  at  BB  is  properly 


118  INORGANIC  CHEMISTRY 

adjusted,  the  flame  will  be  blue  and  non-luminous.  If  the 
openings  at  the  bottom  of  the  burner  are  closed  so  that  no 
air  can  enter,  the  flame  becomes  yellow  in  color  and  luminous. 

The  luminosity  of  the  flame  is  easily  explained.  A  piece 
of  platinum  wire  placed  in  the  blue  flame  of  the  Bunsen 
burner  becomes  white-hot  and  gives  off  light.  If  some  fine 
iron  dust  is  blown  into  it,  the  flame  becomes  momentarily 
luminous.  The  same  effect  may  be  produced  with  charcoal 
dust  or  fine  table  salt.  In  these  experiments  it  is  evident 
that  the  light  comes  from  a  solid  substance  which  has  been 
heated  to  a  white  heat  or  to  incandescence.  The  same 
thing  is  true  of  all  luminous  flames.  In  the  flame  produced 
by  any  of  the  ordinary  illuminants  there  is  a  place  in  the 
flame  where  the  combustion  is  not  complete.  The  heat  de- 
composes some  of  the  gaseous  compounds  and  the  carbon 
is  set  free.  It  is  this  very  finely  divided  carbon  heated  to  in- 
candescence that  gives  off  the  light.  A  gas  like  acetylene, 
which  is  very  rich  in  carbon,  therefore,  gives  more  light  than 
one  like  natural  gas,  which  is  relatively  low  in  carbon.  In 
general,  then,  it  may  be  said  that  light  is  produced  by  a 
solid  substance  which  is  heated  to  incandescence.  In  the 
Welsbach  burner  the  light  comes  from  the  mantle,  the 
material  of  which  is  heated  by  the  blue  flame  of  the  Bunsen 
burner.  In  the  limelight  the  lime  is  heated  to  incandescence 
by  the  oxyhydrogen  flame,  and  in  the  electric  bulb  the  fila- 
ment is  heated  by  the  electric  current ;  but  the  light  in  each 
case  comes  from  the  heated  solid. 

98.  Structure  of  Flames.  The  luminous  flame  has  several 
distinct  parts,  as  can  readily  be  seen  in  the  flame  of  the 
candle.  A  vertical  section  of  the  candle  flame  is  represented 
in  Fig.  78.  Around  the  wick  there  is  a  dark  cone  A  filled 
with  combustible  gases  formed  from  the  melted  wax,  which 


CARBON 


119 


FIG.  78.—  A  ver- 
tical section  of  can- 
dle flame  showing 
the  three  zones. 


do  not  burn  because  there  is  no  oxygen  present.  It  was  from 
this  cone  that  the  gas  was  drawn  in  Fig.  76.  Above  the  dark 
cone  is  the  luminous  part  of  the  flame  B. 
Here  the  oxygen  is  insufficient  for  complete 
combustion,  but  the  temperature  is  suffi- 
ciently high  to  decompose  some  of  the  gas 
and  liberate  small  particles  of  carbon.  This 
liberated  carbon  heated  by  the  burning  gas 
makes  the  flame  luminous.  A  piece  of  crayon 
held  in  this  part  of  the  flame  will  at  once  be 
coated  with  carbon.  The  exterior  cone  C 
is  almost  invisible,  because  here  there  is 
plenty  of  oxygen  and  combustion  is  complete, 
and  all  the  carbon  is  burned  to  carbon  di- 
oxide. These  three  regions  will  be  found 
in  all  illuminating  flames, 
whatever  their  shape,  as 
can  be  seen  by  carefully  examining  the 
flat  flame  of  the  ordinary  gas  burner  or 
the  flame  of  the  kerosene  lamp.  In  the 
non-luminous  flame  of  the  Bunsen  burner 
two  principal  regions  are  easily  distin- 
guished, an  inner  cone  A  of  unburned  gas 
and  an  outer  cone  B,  where  the  combus- 
tion is  complete.  The  hottest  part  of  the 
flame  is  just  above  the  inner  cone  A 
(Fig.  79). 

99.  Kindling  Temperature  of  Gases. 
Gases,  like  other  substances,  must  be  kept 
at  their  kindling  temperature  in  order  to 
burn.  If  they  are  cooled  below  the  kindling  temperature, 
the  flame  is  extinguished.  If  a  piece  of  wire  gauze  is  pressed 


FIG.  79.— A  verti- 
cal section  of  the 
Bunsen  flame  show- 
ing the  two  zones. 


120 


INORGANIC  CHEMISTRY 


down  on  the  flame  of  a  Bunsen  burner,  the  flame  remains 
below  the  gauze,  although  the  gas  passes  freely  through 
it  and  escapes.  If  the  gas  is  now  extinguished  and  then 
relighted  above  the  gauze,  it  will  burn 
above  but  not  beneath  (Fig.  80).  The 
explanation  is  that  the  gauze  conducts 
away  the  heat  rapidly  enough  to  cool 
the  gas  below  its  kindling  temperature. 
100.  Davy's  Safety  Lamp.  The 
miner's  feafety  lamp  depends  upon  this 


FIG.  80.  —  Showing  how  wire  gauze  cools  the  gas  be- 
low the  kindling  point. 


FIG.      81.   —  Davy's 
safety  lamp. 


principle.  It  is  an  oil  lamp  surrounded  by  fine  wire  gauze 
(Fig.  81).  In  a  mine  where  there  are  explosive  gases  the 
lamp  will  continue  to  burn,  and  some  of  the  gas  may  even 
enter  the  lamp  and  burn  inside ;  but  since  the  wire  gauze 
prevents  the  gas  on  the  outside  from  being  heated  to  its 
kindling  temperature,  explosions  are  often  prevented. 

EXERCISES 


Ex.  66.     Heat  some  sawdust,  a  piece  of  cotton,  a  bit  of  bone,  a  piece 
of  lean  meat,  and  some  sugar  or  starch  in  test  tubes  or  in  a  covered 


CARBON 


121 


iron  dish.  What  residue  do  you  get  in  these  experiments?  Hold  a 
piece  of  crayon  in  the  flame  of  a  candle.  What  is  the  black  coating 
on  the  crayon?  What  do  these  experiments  show  as  to  the  distribu- 
tion of  carbon?  Name  some  other  substances  containing  carbon. 
Give  the  properties  of  carbon.  What  is  formed  when  carbon  burns? 
Tell  what  you  can  about  the  following  forms  of  carbon :  (1)  diamond, 
(2)  graphite,  (3)  wood  char- 
coal, (4)  animal  charcoal, 
(5)  coal,  (6)  lampblack. 

Ex.  67.  Mix  a  teaspoon- 
ful  of  copper  oxide  with  an 
equal  quantity  of  powdered 
charcoal  and  place  it  in  a  hard 
glass  test  tube.  Arrange  as 
in  Fig.  82,  allowing  the  end 
of  the  rubber  tubing  to  dip 
into  a  bottle  containing  lime- 
water.  Heat  the  tube  cau- 
tiously until  gas  ceases  to  be 
evolved,  and  remove  tubing 
from  the  water.  What  has 
happened  to  the  limewater? 
To  the  copper  oxide?  Ex- 
plain the  change  in  the  cop- 
per oxide  and  write  the  reaction.  What  kind  of  agent  is  carbon  ?  Is 
any  commercial  use  made  of  this  property  of  carbon  ? 

Ex.  68.  Put  half  a  test  tube  full  of  bone  black  into  a  small  flask 
and  pour  in  about  two  ounces  of  water  to  which  have  been  added  a 
few  drops  of  indigo  or  litmus.  Mix,  heat  gently  for  a  few  minutes,  and 
filter.  Has  anything  happened  to  the  color?,.  Name  an  industry 
in  which  animal  charcoal  is  used  as  a  decolorizer. 

Fill  a  test  tube  half  full  of  powdered  wood  charcoal.  Add  2  cc. 
of  a  solution  of  hydrogen  sulphide.  Cork  the  tube  securely  and 
shake  it  thoroughly  for  some  time.  Let  it  stand  for  fifteen  minutes ; 
then  remove  the  stopper  and  note  whether  the  odor  is  less  offensive. 
Is  charcoal  ever  used  as  a  deodorizer? 

Ex.  69.  Place  some  pieces  of  soft  coal  in  a  small  porcelain  crucible 
and  connect  it  with  the  bowl  of  a  clay  pipe,  making  the  connection 


FIG.  82.  —  Heating  charcoal  and  copper 
oxide  and  passing  the  resulting  gas  into  lime- 
water. 


122 


INORGANIC   CHEMISTRY 


tight  with  clay  (Fig,  83).  Heat  in  the  Bunsen  flame.  Does  any- 
thing escape  through  the  stem  of  the  pipe  ?  Will  the  escaping  material 
burn?  When  all  the  volatile  matter  has  been  expelled,  examine  the 

residue  in  the  crucible.  What  is  it? 
Explain  how  illuminating  gas  is  manu- 
factured. How  is  coke  produced  ? 

Ex.  70.  Does  the  blue  flame  of  the 
Bunsen  burner  give  much  light  ?  Hold 
a  piece  of  platinum  wire  in  the  flame. 
Is  more  light  produced?  Sprinkle  a 
little  charcoal  dust  or  some  fine  salt 
in  the  flame.  Does  it  make  the  flame 
more  luminous  ?  To  what  is  the  lumi- 
nosity of  the  flame  due  ?  Why  is  the 
acetylene  flame  more  luminous  than 
that  of  natural  gas?  What  makes  the 
light  in  the  Welsbach  burner?  Draw 
a  diagram  of  the  flame  of  a  candle  and 
indicate  the  different  zones.  What 
makes  the  flame  of  the  candle  lumi- 
nous? 

Ex.  71.  Do  all  substances  burn  with  a  flame?  What  substances 
produce  flames?  How  can  you  show  that  the  flame  of  a  candle  is 
due  to  a  burning  gas?  Light  a  candle  and  allow  it  to  burn  a  few 
minutes.  Light  a  match, -blow  out  the  candle,  and  apply  the  match 
to  the  ascending  smoke.  Repeat,  noting  whether  the  candle  can  be 
lighted  at  a  distance  from  the  wick.  Explain  how  this  is  possible. 
Why  does  wood  burn  with  a  flame  while  charcoal  does  not  ? 

Ex.  72.  Press  a  piece  of  wire  gauze  halfway  down  on  a  Bunsen 
flame  (Fig.  80).  Does  the  flame  pass  through  the  gauze  ?  Does  any 
unburned  gas  pass  through  ?  Turn  off  the  gas,  then  turn  it  on  again 
and  light  it  above  the  gauze  (Fig.  80).  Does  the  gas  burn  below 
the  gauze  ?  Explain  the  results  in  these  two  cases.  How  is  the  miner's 
safety  lamp  constructed?  Explain  how  it  prevents  explosions.  Do 
gases  have  a  definite  kindling  temperature  ? 


FIG.  83.  —Apparatus  to  illustrate 
the  manufacture  of  illuminating  gas 
and  coke. 


CHAPTER  XII 
CARBON   COMPOUNDS 

101.  Carbon  Burns  to  Carbon  Dioxide.     If  a  piece  of  char- 
coal is  ignited  and  placed  in  a  bottle  containing  oxygen,  it 
will  burn  violently,  throwing  off  a  shower  of  sparks,  and  the 
bottle  will  be  filled  with  a  gas  having  a  slightly  pungent 
odor.     Limewater  placed  in  the  bottle  becomes  milky,  and  a 
white  precipitate  settles  out.     The  carbon  has  burned  to 
carbon  dioxide,  which  fact  may  be  expressed  thus  : 

C  +  2  O  ->-  CO2. 

This  behavior  with  limewater  is  a  test  for  carbon  dioxide, 
since  no  other  gas  acts  in  this  way.  If  the  products  of  com- 
bustion from  a  gas  jet,  from  burning  alcohol,  or  from  the 
flame  of  a  candle  or  kerosene  lamp  are  collected. by  holding 
an  empty  wide-mouth  bottle  over  the  flame  for  a  moment, 
and  then  tested  with  limewater,  it  will  be  found  that  the 
milkiness  is  produced  in  each  case.  In  other  words,  when 
any  substance  containing  carbon  is  burned,  the  carbon  is  oxi- 
dized to  carbon  dioxide. 

102.  Carbonic  Acid.     If  a  little  water  is  added  to  a  bottle 
in  which  charcoal  has  been  burned,  the  carbon  dioxide  will 
dissolve  in  it.    This  water  will  turn  blue  litmus  paper  red, 
and  has  a  very  faintly  sour  taste,  which  suggests  that  an  acid 
is  present.     When  carbon  dioxide  is  dissolved  in  water,  it 
forms  a  weak,  unstable  acid  according  to  the  equation, 


This  compound,  H2CO3,  is  carbonic  acid.  It  is  so  unstable  that 

123 


124 


INORGANIC  CHEMISTRY 


even  at  low  tenrpwatures  it  breaks  up  into  carbon  dioxide 
and  water ;   thus  : 


(Compare  with  the  reaction  of  sulphur  dioxide  and  water 
(83).)  The  instability  of  carbonic  acid  makes  it  impossible 
to  obtain  it  free  from  water.  Many  of  its  salts,  which  are 
called  carbonates,  are  known.  The  carbonates  are  stable 
compounds  and  most  of  them  are  insoluble  in  water.  Lime- 
stone, marble,  and  chalk  are  all  calcium  carbonate  (CaCO3), 
the  salt  formed  by  replacing  the  hydrogen  of  carbonic  acid 
with  metal  calcium.  Washing  soda,  or  sodium  carbonate 
(Na2CO3),  is  another  well-known  salt  of  carbonic  acid. 

103.   Preparation   of   Carbon   Dioxide.     When   a   strong 
acid  like  sulphuric  acid  acts  on  a  carbonate,  the  carbonic 

acid  is  set  free;  but  since  the 
latter  is,  for  the  most  part,  im- 
mediately decomposed  into  car- 
bon dioxide  and  water,  the  reac- 
tion is  usually  written  thus  ; 

Na*C03  +  H2S04  ->• 

Na*SO4  +  CO2  +  H2O. 

This  reaction  may  be  used  for 
the  preparation  of  carbon  di- 
oxide, but  the  more  usual  labo- 
ratory method  is  by  the  action 
of  hydrochloric  acid  on  marble, 
or  ordinary  limestone.  Hydro- 
chloric acid  is  used  because  its 
compound  with  calcium  is  soluble  in  water  (Fig.  84),  while 
calcium  sulphate  is  not.  The  reaction  is  indicated  thus  : 

CaCO3  +  2  HC1  ->•  CaCl2  +  CO2  +  H2O. 


FIG.  84.  — Production  of  carbon 
dioxide  from  limestone  and  hydro- 
chloric acid. 


CARBON  COMPOUNDS 


125 


104.  Properties  of  Carbon  Dioxide.  Carbon  dioxide  is 
a  colorless  gas  with  a  slightly  pungent  odor  and  acid  taste. 
It  is  one  and  one  half  times  heavier  than  air. 
It  can  be  poured  from  one  vessel  to  another. 
At  ordinary  temperature  and  pressure  water 
dissolves  its  own  volume  of  carbon  dioxide. 
Under  increased  pressure  water  dissolves  much 
more  of  the  gas,  and  as  the  pressure  is  re- 
leased the  gas  escapes.  Soda  water  is  made 
by  forcing  carbon  dioxide  into  water  under 


FIG.  85. —Si- 
phon bottle  used 
to  hold  carbon- 
ated  water. 


pressure,  and  the  escape 
of  the  gas  as  the  pressure 
is  released  accounts  for 
the  effervescence  and  froth- 
ing when  it  is  drawn  from  the  fountain 
or  a  siphon  bottle  (Fig.  85).  Many 
mineral  waters,  as  well  as  manufactured 
beverages,  sparkle  and  effervesce  for  the 
same  reason.  Carbon  dioxide  is  some- 
what easily  liquefied  and  is  sold  in  large 
quantities  in  steel  cylinders.  Liquid  car- 
bon dioxide  is  used  in  the  manufacture 
of  soda  water  and  to  produce  very  low 
temperatures.  Many  of  the  small  fire 
extinguishers  (Fig.  86)  contain  baking 
soda  and  sulphurio  'acid  so  arranged 
that  they  can  be  mixed  at  the  moment 
needed.  The  mixture  of  water  and  CC>2 
under  pressure  will  often  put  out  a  small 
blaze  and  prevent  a  serious  fire.  Air 

containing  3  to  4  per  cent  of  carbon  dioxide  will  extinguish 

small  flames. 


FIG.  86.  —  Section  of 
fire  extinguisher. 


126  INORGANIC  CHEMISTRY 

Carbon  dioxide  will  not  burn  because  it  is  itself  the  product 
of  the  complete  combustion  of  carbon.  Carbon  dioxide  will  not 
support  combustion  nor  sustain  life.  It  is  not  poisonous, 
but  animals  placed  in  it  die  of  suffocation.  Water  contain- 
ing carbon  dioxide  will  dissolve  many  substances  which  are 
but  slightly  soluble  in  pure  water.  This  property  of  car- 
bonated water  is  due  to  the  presence  of  carbonic  acid,  which 
is  formed  when  carbon  dioxide  dissolves  in  water.  All  soil 
water  contains  carbonic  acid,  which  is  an  important  factor  in 
changing  the  insoluble  constituents  of  the  soil  into  soluble 
forms. 

105.  Carbon  Dioxide  and  Plant  Life.  It  has  been  shown 
that  carbon  dioxide  comprises  about  .03  per  cent  to  .04  per 
cent  of  the  atmosphere,  or  three  to  four  parts  in  ten  thou- 
sand. This  carbon  dioxide  is  the  sole  source  of  the  carbon 
found  in  green  plants,  and,  since  all  animals  live  directly 
or  indirectly  upon  plants,  it  is  the  source  of  all  the  carbon 
found  in  both  animal  and  vegetable  tissues.  Green  plants 
have  the  power  of  abstracting  carbon  from  carbon  dioxide  and 
uniting  it  with  other  substances  to  form  the  various  complex 
compounds  found  in  the  plants.  This  power  of  the  green 
plant  is  dependent  upon  the  green  coloring  matter,  or  chloro- 
phyll, which  is  found  in  the  leaves.  The  first  visible  effect 
of  the  action  of  chlorophyll  is  the  presence  of  starch  in  the 
leaves.  The  chlorophyll  apparently  brings  about  a  reaction 
between  carbon  dioxide  and  water,  which  may  be  represented 
by  the  following  equation  : 

6  CO2  +  5  H2O  •>•  C6H10O5  +  12  O. 

starch 

That  green  leaves  decompose  carbon  dioxide  and  liberate 
the  oxygen  can  be  shown  by  a  simple  experiment.     A  quan- 


CARBON   COMPOUNDS 


127 


tity  of  water  is  charged  with  carbon  dioxide  by  running  a  cur- 
rent of  the  gas  from  a  generator  through  it  for  a  few  minutes. 
Some  sprigs  of  mint,  water  cress,  or  some  other  plant  are 
placed  in  a  glass  cylinder  and  covered 
with  carbonated  water.  A  funnel 
and  a  test  tube  filled  with  water  are 
arranged,  as  shown  in  Fig.  87,  so  as 
to  collect  any  gas  which  may  be 
formed.  The  apparatus  is  placed  in 
the  strong  sunlight,  and  after  a  short 
time  bubbles  of  gas  will  arise  and 
replace  the  water  in  the  test  tube. 
When  sufficient  gas  has  collected, 
the  test  with  a  glowing  splint  will 
show  that  it  is  oxygen. 

Sunlight  is  necessary  to  furnish 
the  plant  with  the  energy  required  to 
decompose  the  carbon  dioxide.  When 
carbon  burns  to  carbon  dioxide,  a 
large  amount  of  heat  is  given  off. 
This  heat  is  known  as  the  heat,  of 
formation.  Before  such  a  compound 
as  carbon  dioxide  can  be  decomposed, 

an  amount  of  energy  must  be  provided  which  is  equiva- 
lent to  the  heat  energy  which  was  given  off  when  the  com- 
pound was  formed ;  or,  in  other  words,  an  amount  of  energy 
equivalent  to  the  heat  of  formation  of  the  compound.  The 
plant  derives  this  energy  from  the  sunlight,  and  conse- 
quently the  formation  of  starch  in  the  plant  does  not  go  on 
at  night.  It  will  thus  be  seen  that  without  sunlight  all  life 
would  cease,  for  every  living  thing  is  dependent  either 
directly  or  indirectly  upon  the  decomposition  of  carbon 


FIG.  87.  — The  decompo- 
sition of  carbon  dioxide  and 
liberation  of  oxygen  by  plants. 


128 


INORGANIC  CHEMISTRY 


dioxide  by  plants  (340).  The  process  by  which  plants 
utilize  the  carbon  of  carbon  dioxide  to  form  starch  is  called 
photosynthesis  (341). 

106.  Amount  of  Carbon  Dioxide  in  the  Atmosphere.  The 
percentage  of  carbon  dioxide  in  the  atmosphere  is  so  small 
that  it  might  be  feared  that  the  supply  would  soon  be  ex- 
hausted. So  great  is  the  bulk  of  the  atmosphere,  however, 
that  it  has  been  calculated  that  the  air  contains  not  less  than 
3,400,000,000,000  tons  of  carbon  dioxide.  This  amounts 
to  28  tons  over  each  acre  of  the  earth's  surface. 


CARBON;  DIOXIDp 
IN  ATMOSPHERE: 


FIG.  38.  —  The  cycle  of  carbon  in  nature. 


107.  Formation  of  Carbon  Dioxide  in  Nature.  The  supply 
of  carbon  dioxide  in  the  atmosphere  is  being  constantly  re- 
newed in  several  ways.  The  burning  of  fuels  of  all  kinds  re^ 


CARBON  COMPOUNDS  129 

suits  in  the  production  of  carbon  dioxide,  as  does  also  the 
decay  of  all  organic  matter.  Fermentations,  such  as  take 
place  in  wines  and  cider,  and  in  breweries  and  distilleries, 
give  rise  to  carbon  dioxide.  It  is  also  given  off  in  the  vicinity 
of  volcanoes  and  from  mineral  springs.  It  is  exhaled  by  the 
breathing  of  all  animals  as  well,  for  it  is  the  product  of  the 
slow  combustion  of  carbon  in  the  animal  body.  Carbon 
dioxide  sometimes  accumulates  at  the  bottom  of  wells,  in 
silos,  and  in  mines,  since  it  is  often  formed  in  such  places 
more  rapidly  than  it  can  be  removed  by  diffusion.  Many 
deaths  have  occurred  from  suffocation  in  such  places. 
Carbon  dioxide  is  called  choke  damp  by  the  miners.  The 
production  of  carbon  dioxide  in  the  various  ways  mentioned 
is  so  nicely  balanced  by  the  decomposition  of  this  gas  by 
green  plants,  that  the  amount  of  carbon  dioxide  and  of  oxy- 
gen in  the  air  scarcely  varies.  The  cycle  of  carbon  in  nature 
is  indicated  in  Fig.  88. 

108.  Carbon  Monoxide.  When  a  substance  containing 
carbon  is  burned  in  an  insufficient  supply  of  air,  carbon  monox- 
ide (CO)  is  formed.  If  carbon  dioxide  is  passed  over  highly 
heated  carbon,  a  reaction  takes  place  which  is  represented  by 
the  following  equation : 

CO2  +  C  -^  2  CO. 

Carbon  monoxide  is  formed  during  the  burning  of  hard  coal 
in  a  stove  or  grate.  At  the  lower  part  of  the  fire,  where  there 
is  free  access  of  air,  the  carbon  burns  to  carbon  dioxide,  but 
as  it  passes  up  through  the  heated  coal  the  dioxide  is  par- 
tially reduced  to  carbon  monoxide.  When  the  monoxide 
escapes  from  the  top,  it  again  combines  with  oxygen  and 
burns  with  the  blue  flame  always  noticed  above  a  mass  of 
EV.  CHEM. — 9 


130  INORGANIC   CHEMISTRY 

burning  hard  coal.  Pure  carbon  monoxide  is  a  colorless, 
tasteless,  and  odorless  gas,  which  burns  with  a  pale  blue 
flame.  It  is  exceedingly  poisonous.  It  is  the  most  dangerous 
gas  given  off  from  coal  stoves,  and  great  precaution  should 
be  taken  to  prevent  its  escape  into  the  room. 

109.  Water  Gas.     In  the  manufacture  of  coal  gas  it  is 
customary  to  take  advantage  of  the  fact  that  highly  heated 
carbon  will  decompose  water.     After  all  the  volatile  matter 
has  been  driven  off  from  coal,  and  while  the  coke  is  still 
very  hot,  steam  is  turned  into  the  retorts  with  the  result  that 
the  following  reaction  takes  place  : 

H2O  +  C  -^  CO  +  H2. 

This  mixture  of  hydrogen  and  carbon  monoxide  is  known 
as  water  gas.  Only  a  limited  quantity  of  the  gas  can  be 
made,  as  the  coke  is  soon  cooled  below  the  point  at  which  it 
will  decompose  water.  As  both  hydrogen  and  carbon  mon- 
oxide burn  with  a  non-luminous  flame,  water  gas  cannot  be 
used  as  an  illuminating  gas  unless  it  is  first  enriched  by  the  ad- 
dition of  some  petroleum  product  high  in  carbon.  Owing  to 
its  high  percentage  of  carbon  monoxide,  water  gas  is  very  poi- 
sonous. 

110.  Carbon  Bisulphide.     Carbon  forms  one  important 
compound  with  sulphur.     The  two  elements  are  made  to 
combine  in  an  electric  furnace,  the  resulting  compound  being 
carbon  bisulphide,  CS2.     Commercial  carbon  bisulphide  is  a 
yellow  liquid  with  an  offensive  odor.    It  is  poisonous,  volatile, 
and  very  inflammable.     The  equation  for  its  combustion  is 


Carbon  bisulphide  is  insoluble  in  water.     It  dissolves  rubber, 


CARBON   COMPOUNDS  131 

gums,  fats,  camphor,  and  sulphur  (60) .  The  common  rubber 
cement  is  a  solution  of  rubber  in  carbon  bisulphide.  Carbon 
bisulphide  is  used  as  an  insecticide  and  to  exterminate  bur- 
rowing animals  such  as  moles,  woodchucks,  and  gophers. 
As  its  vapor  is  much  heavier  than  air  it  readily  sinks  to  the 
bottom  of  the  burrow. 

111.  Other  Compounds  of  Carbon.  It  has  been  stated 
that  more  than  100,000  compounds  of  carbon  have  been 
prepared.  Most  of  these  compounds  are  of  animal  or  vege- 
table origin,  and  the  study  of  these  numerous  and  complex 
compounds  is  commonly  called  organic  chemistry.  It  was 
formerly  thought  that  these  compounds  could  be  produced 
only  by  life  processes,  but  many  of  them  have  been  produced 
artificially.  It  is  more  convenient,  however,  to  deal  with 
this  subject  after  the  chemistry  of  the  other  common  ele- 
ments has  been  studied.  The  more  common  and  important 
of  the  carbon  compounds  will  be  discussed  in  Part  II  of  this 
text. 

EXERCISES 

Ex.  73.  Ignite  a  piece  of  Charcoal  and  place  it  in  a  bottle  containing 
oxygen.  Note  the  odor  of  th  gas  formed.  Place  a  little  limewater 
in  the  bottle.  What  happens  to  the  limewater?  What  is  the  gas 
formed  by  burning  carbon?  Hold  an  empty  bottle  over  the  flame  of 
a  candle  and  test  it  with  limewater.  What  is  the  result?  Take 
some  limewater  home  with  you  and  test  any  flames  for  carbon  dioxide. 

Ex.  74.  Place  a  little  water  in  the  bottom  of  a  wide-mouth  bottle 
and  burn  a  piece  of  charcoal  in  the  bottle.  Shake  the  bottle  and  test 
the  water  with  litmus  paper.  Is  an  acid  formed  ?  Write  the  equation. 
What  happens  when  the  solution  is  warmed?  Compare  with  the  re- 
actions for  sulphur  dioxide.  Can  carbonic  acid  be  prepared  in  the 
pure  state?  Are  its  salts  (the  carbonates)  stable?  Name  a  common 
carbonate. 


132 


INORGANIC  CHEMISTRY 


Ex.  75.    Arrange  apparatus  as  in  Fig.  84  and  place  several  pieces 
of  marble  or  limestone  in  the  bottle   and   cover  with   water.     Pour 
dilute  hydrochloric  acid  in  the  thistle  tube  and  collect  the  carbon 
dioxide  by  downward  displacement  as  shown  in  the  figure.     What  is 
the  appearance  of  the  gas  ?     What  is  its  odor  and  its  taste  ?     Light  a 
candle,  place  it  in  a  tumbler,  and  pour  a  bottleful  of  carbon  dioxide 
over  it  (Fig.  89).    What  happens  to  the  candle?     Is  CO2  heavier  than 
air?     Place  a  bottle  of   air  mouth  down- 
ward   over    a   bottle    of    carbon    dioxide. 
After  ten  minutes  test  the  contents  of  the 
upper  bottle  for  CO2.     What  is  the  result  ? 
What  effect  does  pressure    have    on    the 
solubility  of  the  gas  in  water  ?     What  use 
is  made  of  this  fact  ?     What  use  is  made 
of   liquid   carbon    dioxide?      How   do   the 
small   fire  extinguishers   work?     Why  will 
carbon   dioxide   not  burn?     Is  it    poison- 
ous ?     Why  do  animals  die  when  placed  in 
it?     Why  does  water   containing  carbon 
dioxide    dissolve  some  minerals  which  are 
insoluble  in  pure  water  ?     How  many  sub- 
stances  can  you  find  at  home  which  are  carbonates  or  contain  car- 
bonates ?    Test  them  with  hydrochloric  acid  and  note  whether  CO2  is 
given  off. 

Ex.  76.  Fill  a  tall  glass  cylinder  with  water  and  cause  carbon 
dioxide  to  bubble  through  it  for  a  few  rrinutes.  Place  several  sprigs 
of  mint  or  water  cress  in  the  cylinder  and  arrange  a  funnel  and  test 
tube  as  shown  in  Fig.  87.  Place  the  apparatus  in  strong  sunlight 
and  when  sufficient  gas  collects  in  the  test  tube  test  for  oxygen  with  a 
glowing  splint.  How  do  green  plants  obtain  their  carbon  ?  Is  chloro- 
phyll necessary  for  this  process  ?  Why  is  sunlight  necessary  to  enable 
the  plant  to  use  the  carbon  of  carbon  dioxide  ?  What  is  heat  of  forma- 
tion? How  much  carbon  dioxide  does  the  atmosphere  contain?  Is 
there  any  danger  of  the  supply  being  exhausted  by  plants?  How  is 
the  supply  of  CO2  in  the  air  renewed  ?  Why  is  it  dangerous  to  go  into 
a  well  or  a  silo  that  has  been  closed  tightly  for  some  time  ?  What 
name  do  the  miners  give  to  carbon  dioxide  ? 


FIG.  89. —Extinguishing 
a  candle  by  pouring  carbon 
dioxide  gas  over  it. 


CARBON  COMPOUNDS  133 

Ex.  77.  What  other  oxide  of  carbon  is  known  ?  Explain  the  forma- 
tion of  this  oxide  in  the  coal  stove.  Reaction?  Why  should  coal 
stoves  and  furnaces  be  gas  tight?  How  is  water  gas  made?  Give 
reaction.  Is  it  a  good  illuminating  gas?  How  can  it  be  improved 
as  an  illuminant?  What  important  compound  does  carbon  form 
with  sulphur?  Reaction?  In  what  experiment  did  you  use  this 
substance?  For  what  purposes  is  carbon  bisulphide  used?  If  there 
is  an  ant  hill  at  home  try  the  following  experiment.  With  a  stick  make 
a  hole  an  inch  or  two  in  diameter  and  a  foot  deep  in  the  ant  hill.  Pour 
in  two  ounces  of  carbon  bisulphide  and  cover  the  hole  with  earth. 
Place  a  piece  of  carpet  or  a  blanket  over  the  ant  hill.  Examine  after 
twelve  hours  and  report. 


CHAPTER   XIII 


LIMESTONE  AND    OTHER  CALCIUM   COMPOUNDS 


112.   Limestone.     One   of   the 

substances  in  nature  is  limestone. 


most   widely   distributed 
It  is  most  familiar  as  the 

,     ordinary      limestone 

used  for  building  pur- 
poses ;  but  marble, 
chalk,  coral,  marl, 
and  shells  are  identi- 
cal in  composition 
with  limestone.  They 
all  consist  largely  of 
the  compound  made 
by  the  combination 
of  the  metal  calcium 
with  carbonic  acid; 
namely,  calcium  car- 
bonate, GaCO3.  In 
marble  the  calcium 
carbonate  exists  as  a 
mass  of  minute  crys- 
tals. Chalk  and 
most  limestone  are 
not  crystalline,  but  often  show  by  their  structure  that  they 
have  been  derived  from  shells.  The  transparent  crystals  of 
calcite  and  Iceland  spar  (Fig.  91)  are  very  pure  forms  of  cal- 

134 


FIG.  90.  —  A  limestone  cliff. 


LIMESTONE   AND   OTHER   CALCIUM   COMPOUNDS  *135 


cium  carbonate.  Calcium  carbonate  is  insoluble  in  water. 
It  is  decomposed  by  most  acids,  with  the  result  that  carbon 
dioxide  is  given  off 
and  the  calcium 
salt  of  the  acid  is 
formed.  (See  103.) 
113.  Manufac- 
ture of  Lime.  When 
calcium  carbonate 
is  strongly  heated, 
carbon  dioxide  is 
driven  off  and  cal- 
cium oxide  remains, 
thus: 


FIG.  91.  —  Crystals  of  calcite. 

Calcium  oxide,  CaO,  is  the  substance  known  as  lime,  also 
called  burnt  lime,  quicklime,  or  caustic  lime.  The  pro- 
cess of  preparing 
lime  is  termed 
"  burning  lime," 
which  is  a  mis- 
nomer, as  burn- 
ing consists  in 
the  uniting  of  a 
substance  with 
oxygen,  while 
this  process  is  a 
decomposition 
and  not  an  oxi- 
dation.  The 

FIG.  92.  —  A  homemade  limekiln.  "  burning  "        of 


136 


INORGANIC  CHEMISTRY 


limestone 


lime  is  one  of  the  oldest  of  chemical  processes  and  has  been 
carried  on  for  at  least  fifty  centuries. 

In  the  older  method  of  preparing  lime  a  fire  of  wood  or 
coal  is  made  at  the  bottom  of  the  limekiln,  which  is  a 

shaft  or  chimney  quite 
commonly  built  in  a  hill- 
side. When  the  limestone 
which  is  placed  on  the  fuel 
is  completely  burned,  it  is 
removed  and  the  kiln  is  re- 
filled. At  the  present  time 
kilns  (Fig.  93)  are  so  built 
that  the  operation  is  con- 
tinuous, limestone  being 
added  at  the  top  of  the 
kiln  and  the  lime  being 
removed  from  the  bottom 
as  fast  as  it  is  formed. 
Lime  is  most  familiar  in 
the  form  of  lump,  or 
builder's, lime.  It  is  often 
ground  to  a  powder  and 
sold  as  ground  lime. 

114.   Slaked     Lime. 
When    lime    is    sprinkled 

with  water,  it  becomes  very  hot,  swells,  and  finally  crumbles 
to  a  white  powder.  This  process  is  called  slaking  the  lime, 
and  the  white  powder  is  known  as  slaked  lime  or  hydrated 
lime.  The  chemical  name  for  it  is  calcium  hydroxide.  The 
change  may  be  represented  thus  : 


FIG.  93.  — A  modern  limekiln. 


CaO  +  H2O  ->-  Ca(OH)2. 


CALCIUM  COMPOUNDS  137 

Calcium  hydroxide,  Ca(OH)2,  is  somewhat  soluble  in 
water,  and  this  solution  is  called  limewater.  It  will  thus 
be  seen  that  calcium  oxide  behaves  toward  water  in  much 
the  same  way  as  do  the  oxides  of  sulphur  and  carbon ;  that 
is,  it  forms  a  chemical  compound  with  the  water.  But  when 
sulphur  trioxide,  for  instance,  is  added  to  water,  the  solution 
has  a  sour  taste  and  it  turns  blue  litmus  paper  red.  Lime- 
water,  on  the  other  hand,  has  an  astringent,  or  alkaline,  taste, 
and  does  not  change  the  color  of  blue  litmus  paper.  On  the 
contrary,  if  the  paper  which  was  turned  red  by  the  acid  is 
placed  in  limewater,  the  blue  color  will  be  restored.  It  will 
be  found  that  there  are  other  oxides  which  behave  in  the 
same  way.  Evidently,  then,  not  all  oxides  form  acids  with 
water,  but  some  form  compounds  with  properties  the  oppo- 
site of  acids. 

Limewater  is  used  in  medicine,  and  as  previously  men- 
tioned is  used  in  the  chemical  laboratory  as  a  test  for  carbon 
dioxide,  with  which  it  forms  the  insoluble  calcium  carbonate, 
the  equation  being 

Ca(OH)2  +  CO2  -^  CaCO3  +  H2O. 

When  considerable  calcium  hydroxide  is  suspended  in  water, 
the  mixture  is  called  milk  of  lime.  Ordinary  whitewash  is 
thin  milk  of  lime. 

Mortar  is  a  thick  paste  made  by  mixing  slaked  lime  and 
sand.  It  sets  or  hardens  partly  owing  to  the  loss  of  water 
by  evaporation,  but  also  because  carbon  dioxide  is  absorbed 
and  the  calcium  hydroxide  is  changed  into  the  carbonate. 
The  same  change  takes  place  in  whitewash  when  it  is  spread 
on  a  wall.  The  hardening  of  plaster  may  be  hastened  by 
burning  charcoal  in  the  room  so  as  to  increase  the  amount 
of  carbon  dioxide  in  the  air. 


138  INORGANIC  CHEMISTRY 

115.  Air-slaked  Lime.     When  lime  is  exposed  to  the  air, 
it  absorbs  moisture  and  slakes.     It  also  absorbs  carbon  diox- 
ide from  the  air  and  changes  to  the  carbonate : 

CaO  +  CO2  ->•  CaCO3. 

Lime  that  has  undergone  this  change  to  the  hydroxide  and 
carbonate  is  said  to  be  air-slaked  and  is  of  no  value  for 
making  mortar.  Fires  are  known  to  have  been  caused  by 
the  heat  generated  by  the  action  of  moisture  on  lump  lime. 
The  agricultural  uses  of  lime  are  discussed  in  Chapter  LV. 

116.  Cement.     Portland  cement  is  made  by  mixing  lime- 
stone and  clay,  in  the  proper  proportions,  and  heating  them 
strongly  until  the  mass  begins  to  melt.     The  clinker  formed 
in  this  way  is  ground  to  fine  powder,  which  is  the  cement. 
Occasionally  an  impure  limestone  is  found  which  contains 
the  right  quantity  of  clay  and  sand,  and  this  is  burned 
directly  to  make  the  so-called  natural  cement.     When  cement 
is  moistened  it  sets  to  a  hard,  stone-like  mass.     Mixed  with 
sand  and  stone  it  forms  concrete,  which  is  rapidly  taking 
the  place  of  stone  in  many  building  operations.     The  chemi- 
cal changes  which  take  place  in  cement  are  not  understood. 

117.  Calcium.     The  element  calcium   is  the  fifth  most 
abundant  element  in  nature,  but  it  is  never  found  uncombined. 
It  is  seldom  seen  outside  of  chemical  laboratories.     It  is  a 
silver-white  metal,  soft  enough  to  be  cut  with  a  knife.     It 
will  burn  to  the  oxide  (Ca  +  O  ->-  CaO),  which  is  the  same 
compound  as  that  formed  by  heating  the  carbonate.     It 
decomposes  water  at  ordinary  temperatures,  forming  the  hy- 
droxide and  giving  off  hydrogen,  thus  : 

Ca  +  2  H2O  ->-  Ca(OH)2  +  2  H. 

When  steam  was  passed  over  hot  zinc,  as  was  seen  in  Chap- 
ter II,  the  metal  extracted  the  oxygen  from  the  water  to  form 


CALCIUM  COMPOUNDS  139 

the  oxide  and  set  free  both  atoms  of  hydrogen.  When  cal- 
cium acts  upon  the  water  at  ordinary  temperatures,  it  liber- 
ates only  one  atom  of  hydrogen  from  the  molecule  of  water, 
and  the  oxygen  and  the  remaining  hydrogen  atom  unite  with 
the  metal.  The  change  may  be  represented  thus : 

H— O— H  /OK      K 

Ca  +  -»-  Ca^         + 

H— O— H  X)H      H 

The  calcium  atom,  being  bivalent,  has  replaced  one  hydrogen 
atom  from  each  of  two  molecules  of  water.  The  group  OH, 
which  may  be  said  to  be  water  with  one  hydrogen  atom  re- 
moved, is  of  common  occurrence  in  chemical  compounds  and 
has  been  named  hydroxyl. 

118.  Calcium  sulphate  occurs  in  large  quantities  and  is 
widely  distributed  in  the  substance  known  as  gypsum,  which 
has  the  formula,  CaSO4  •  2  H2O.  The  two  molecules  of  water 
set  off  by  the  period  in  the  formula  represent  the  water  of 
crystallization.  Although  the  water  of  crystallization  can 
be  driven  off  by  heat,  there  is  good  reason  to  believe  that  it 
13  in  chemical  combination  with  the  rest  of  the  compound. 
Water  of  crystallization  is  not  apparent  as  moisture.  It  is 
in  some  way  essential  to  the  crystalline  form,  in  which  it  is 
always  present  in  a  definite  proportion.  The  molecule  of 
gypsum  always  crystallizes  with  two  molecules  of  water. 

Gypsum  occurs  as  white  masses  or  as  transparent  crystals. 
It  is  slightly  soluble  in  water,  one  part  dissolving  in  400  parts 
of  water.  When  heated  it  loses  part  of  its  water  of  crystalli- 
zation and  is  known  as  plaster  of  Paris.  When  water  is  added 
to  plaster  of  Paris,  the  lost  water  is  taken  up  again,  and  the 
material  is  changed  back  to  gypsum  and  sets  as  a  hard,  com- 
pact mass.  Plaster  of  Paris  is  used  in  coating  walls,  in 


140 


INORGANIC  CHEMISTRY 


making  stucco,  and  in  making  casts  and  reproductions  of 
statuary  and  small  objects.  If  the  gypsum  is  heated  too 
strongly,  the  plaster  is  spoiled  and  will  not  set. 

119.  Hardness  of  Water.  In  Chapter  II  mention  was 
made  of  temporary  and  permanent  hardness  of  water,  and  it  is 
now  possible  to  explain  these  phenomena.  Temporary  hard- 
ness is  caused  for  the  most  part  by  the  presence  of  calcium 
carbonate  in  the  water.  Calcium  carbonate  will  not  dissolve 
in  pure  water,  but  will  do  so  to  a  limited  extent  in  water  con- 
taining carbon  dioxide.  This  is  due  to  the  formation  of  acid 
calcium  carbonate  Ca(HCO3)2,  thus  : 

CaCO3  +  H2CO3  ->-  Ca(HCO3)2. 

In  acid  calcium  carbonate  it  is  supposed  that  the  atom  of 
calcium  replaces  one  hydrogen  atom  from  each  of  two  mole- 
cules of  carbonic  acid. 
As  most  natural 
waters  contain  car- 
bon dioxide,  this 
compound  is  gen- 
erally present  in 
water.  It  is  very 
unstable  and  when 
heated  is  decom- 
posed into  ordinary 
calcium  carbonate,  carbon  dioxide,  and  water : 


FIG.  94.  —  A  cone  built  up  from  deposits  made  by 
carbonated  spring  water. 


Ca(HCO3)2  ->-  CaC03  +  CO2  +  H2O. 

This  reaction  explains  why  boiling  the  well  water  causes  a 
deposit  of  calcium  carbonate  and  makes  the  water  less  hard. 
On  a  large  scale  it  is  not  practicable  to  boil  the  water  to 
soften  it,  and  the  same  result  is  brought  about  by  adding 


CALCIUM  COMPOUNDS  141 

just  sufficient  slaked  lime  to  convert  the  acid  carbonate  into 
the  normal  carbonate,  as  shown  in  the  following  equation  : 

Ca(HCO3)2  +  Ca(OH)2  ->-  2  CaCO3  +  2  H2O. 

Hardness  of  water  is  not  entirely  due  to  calcium  com- 
pounds. Magnesium  (Chapter  XXII)  is  usually  associated 
with  calcium  in  nature,  and  part  of  the  hardness  of  water  is 
usually  due  to  magnesium  compounds,  which  act  in  much  the 
same  way  as  do  the  compounds  of  calcium. 

Permanent  hardness  of  water  is  due  to  the  presence  of 
gypsum  in  solution,  a  compound  which  is  not  precipitated  by 
boiling.  To  remove  calcium  sulphate  ordinary  washing  soda 
(sodium  carbonate)  is  added,  and  the  following  reaction 
takes  place  : 

CaSO4  +  Na2CO3  •>•  CaCO3 


The  calcium  carbonate  being  insoluble  is  precipitated  and  the 
sodium  sulphate  (N^SC^)  which  stays  in  solution  is  not  ob- 
jectionable. Such  a  chemical  change  as  the  one  repre- 
sented in  this  reaction  is  called  a  double  decomposition.  It 
will  be  noticed  that  metals  have  changed  places  in  the  salts. 
The  change  might  be  represented  thus  — 

Ca\xSO4 


It  is  a  general  rule  of  chemistry  that  when  two  compounds 
in  solution  are  mixed,  their  component  parts  rearrange  them- 
selves to  form  the  most  insoluble  compound  possible,  and  of 
course  the  insoluble  compound  is  then  precipitated.  Cal- 
cium carbonate,  being  the  most  insoluble  compound  possible 
in  this  mixture,  is  precipitated,  and  the  sodium  sulphate, 
being  very  soluble,  remains  in  solution. 


142  INORGANIC  CHEMISTRY 

In  the  softening  of  water  for  technical  purposes  the  water 
is  carefully  analyzed  and  the  proper  amount  of  calcium 
hydroxide  is  first  added  to  precipitate  the  carbonates.  After 
a  short  time  the  sodium  carbonate  is  added  to  remove  the 
other  calcium  and  magnesium  salts.  '  The  household  methods 
for  softening  water  are  discussed  in  Chapter  XL VIII. 


EXERCISES 

Ex.  78.  Place  two  or  three  thin  chips  of  marble  on  a  wire  gauze 
and  heat  them  ten  minutes  in  the  full  flame  of  the  burner.  Compare 
with  an  unheated  bit  of  marble.  What  is  the  composition  of  the 
marble  ?  What  change  took  place  upon  heating  ?  Write  the  reaction. 
What  substances  can  you  name  that  are  calcium  carbonate?  Can 
you  name  anything  in  your  home  that  is  composed  of  calcium  carbon- 
ate ?  How  is  lime  made  commercially  ? 

Ex.  79.  Lay  one  of  the  heated  chips  of  marble  from  the  above 
experiment  on  a  piece  of  red  litmus  paper  and  on  another  piece  of 
the  same  paper  place  a  bit  of  unchanged  marble.  Moisten  both  pieces 
and  describe  what  happens.  Is  there  any  difference  in  the  effect  of 
the  two  pieces  of  stone  on  the  litmus  paper? 

Ex.  80.  Place  a  lump  of  quicklime  in  a  beaker  and  moisten  with 
hot  water.  Watch  and  describe  the  result.  Write  the  reaction  for 
the  change  in  the  lime.  Fill  the  beaker  with  water  and  stir.  When 
the  solid  settles,  decant  the  clear  liquid  into  a  clean  bottle.  Is  the 
calcium  hydroxide  soluble?  Test  a  portion  of  the  limewater  with 
blue  and  red  litmus  papers.  What  is  the  effect?  How  does  the 
compound  of  calcium  oxide  and  water  compare  with  the  compound  of 
sulphur  dioxide  and  water?  What  is  meant  by  milk  of  lime?  By 
whitewash?  What  is  mortar?  What  makes  mortar  set?  What  is 
meant  by  air-slaked  lime  ?  Is  it  of  any  value  for  building  purposes  ? 
Tell  what  you  can  about  the  manufacture  and  uses  of  Portland  cement. 
What  are  natural  cements  ?  Report  on  anything  at  home  that  is  built 
with  Portland  cement  or  concrete. 

Ex.  81.  Describe  the  element  calcium.  What  compound  is  formed 
when  it  burns?  Give  the  equation  for  the  reaction  of  calcium  on 


CALCIUM  COMPOUNDS  143 

water.  (Note  to  the  teacher.  Metallic  calcium  may  be  obtained  at 
a  moderate  cost  from  some  of  the  supply  houses.  It  will  be  well  to 
perform  the  experiment  of  liberating  hydrogen  from  water  by  means 
of  metallic  calcium  if  possible.)  Does  calcium  replace  all  the  hydro- 
gen of  water?  What  name  is  given  to  the  group  OH  in  chemistry? 
How  many  hydroxyl  groups  unite  with  one  atom  of  calcium  ? 

Ex.  82.  Examine  crystals  of  calcium  sulphate.  What  is  the  for- 
mula ?  The  common  name  ?  What  happens  to  gypsum  when  heated  ? 
Mix  plaster  of  Paris  to  a  thick  paste  with  water.  Rub  a  little  vaseline 
or  lard  over  the  surface  of  a  button  and  press  the  button  into  the  sur- 
face of  the  moist  plaster.  When  the  plaster  has  hardened,  remove 
the  button  and  describe  the  result.  What  made  the  plaster  of  Paris 
set  ?  What  uses  can  you  give  for  plaster  of  Paris  ? 

Ex.  83.  Dilute  a  little  limewater  with  an  equal  volume  of  distilled 
water.  Pass  carbon  dioxide  into  the  solution.  Does  a  precipitate 
form  ?  Continue  the  experiment  and  note  if  the  precipitate  disappears. 
Write  two  equations,  one  for  each  change.  Boil  a  portion  of  this  liquid. 
What  happens?  Explain  the  reappearance  of  the  precipitate.  Boil 
some  well  water  from  home.  Does  a  precipitate  form?  Show  how 
this  experiment  explains  temporary  hardness  of  water.  To  another 
portion  of  the  solution  formed  above  by  passing  carbon  dioxide  into 
limewater  add  a  fresh  portion  of  limewater.  What  result  do  you 
obtain?  How  can  lime  be  used  to  remove  temporary  hardness  of 
water  ? 

Ex.  84.  To  the  well  water  which  has  been  boiled  to  remove  the 
temporary  hardness  add  sodium  carbonate  (washing  soda).  Is  a 
precipitate  formed?  Explain  how  permanent  hardness  is  removed 
from  water.  Give  the  reaction.  What  is  meant  in  chemistry  by  a 
double  decomposition? 


CHAPTER  XIV 
SALT:    CHLORINE  AND   SODIUM 

120.  SALT  is  familiar  to  everyone  as  a  white  solid  which, 
upon  close  examination,  is  seen  to  consist  of  cubical  crystals. 
It  is  widely  distributed.  It  is  found  in  solution  in  sea  water 
to  the  extent  of  3.5  per  cent,  and  in  some  countries  all  the 
table  salt  is  obtained  from  this  source.  The  water  of  Great 


FIG.  95.  —  The  making  of  salt  by  the  evaporation  of  sea  water  in  France. 

Salt  Lake  contains  over  20  per  cent  of  salt.  The  substance 
occurs  in  many  places  as  rock  salt,  and  is  often  mined  in 
large  blocks  and  sold  in  this  form  or  purified  for  table  use. 
Much  of  the  salt  of  commerce  is  obtained  by  drilling  wells 
into  the  salt  deposits,  and  introducing  water,  which  dis- 
solves the  salt,  forming  a  brine  which  is  pumped  out  and 
evaporated. 

The  appearance  and  taste  of  salt  are  familiar.     Water 
dissolves  35  per  cent  of  its  own  weight  of  salt,  the  substance 

144 


SALT  :    CHLORINE  AND  SODIUM  145 

being  nearly  as  soluble  in  cold  water  as  in  hot,  in  which 
respect  it  differs  from  most  solids.  When  it  is  pure  it  re- 
mains dry  on  exposure  to  the  air,  but  it  usually  contains  a 
little  calcium  or  magnesium  chloride  and  hence  attracts 
moisture.  In  addition  to  its  well-known  uses,  it  is  the  chief 
source  of  the  compounds  of  sodium  and  chlorine. 

121.  Action  of  Sulphuric  Acid  on  Salt.     When  sulphuric 
acid  is  poured  upon  common  salt,  a  gas  is  given  off  which 
has  a  strong,  irritating  odor.     It  fumes  strongly  in  the  air, 
and  a  burning  candle  thrust  into  it  is  immediately  extin- 
guished.    This  gas  is  extremely  soluble  in  water,  one  volume 
of  water  dissolving  over  500  volumes  of  the  gas.     Formerly 
this  gas  was  called  spirit  of  salt  because  it  was  prepared  from 
salt. 

The  solution  of  the  gas  in  water  is  strongly  acid.  It  is 
wry  sour  and  turns  blue  litmus  paper  red.  Its  acid  properties 
were  early  recognized,  and  it  received  the  name  of  muriatic 
acid.  This  solution  will  be  found,  upon  comparison,  to  be 
identical  with  the  hydrochloric  acid  of  the  laboratory,  which 
is  in  reality  a  solution  of  hydrochloric  acid  containing  about 
40  per  cent  of  the  gas. 

122.  Composition  of  Hydrochloric  Acid.     If  the  solution 
of  hydrochloric  acid  is  poured  upon  zinc,  hydrogen  will  be 
evoked  just  as  it  is  when  sulphuric  acid  and  zinc  are  used. 
It  is  fair  to  assume,  therefore,  that  hydrochloric  acid  con- 
tains hydrogen  as  one  of  its  elements. 

If  another  portion  of  strong  hydrochloric  acid  solution  is 
placed  in  an  apparatus  like  that  shown  in  Fig.  96,  with  a 
quantity  of  manganese  dioxide,  and  the  flask  is  gently 
heated,  a  gas  is  evolved  which  has  a  yellow-green  color  and 
an  irritating  odor.  This  gas  was  discovered  by  Scheele  in 
1774.  About  1810  the  English  chemist  Sir  Humphry 

EV.    CHEM.  —  10 


146 


INORGANIC  CHEMISTRY 


Davy  proved  it  to  be  an  element  and  named  it  chlorine 
because  of  its  color.  This  gas  also  evidently  came  from 
the  hydrochloric  acid,  since  the  manganese  dioxide  and 

water    alone    will   not   pro- 
duce it. 

If  a  mixture  of  chlorine 
and  hydrogen  is  exposed  to 
strong  sunlight  or  the  light 
from  burning  magnesium,  it 
explodes,  and  the  hydrogen 
and  chlorine  combine  to  form 
hydrochloric  acid  gas.  This 
method  of  synthesizing  hy- 
drochloric acid  shows  that  it 
contains  the  two  elements 
hydrogen  and  chlorine  and 
t  IG.  96.  -  Apparatus^  the  production  of  nothing  else.  If  the  combi- 
nation were  brought  about 

in  a  eudiometer  (Fig.  54),  it  would  be  found  that  ex- 
actly equal  volumes  of  the  two  gases  combine.  As  chlorine 
is  35.46  times  as  heavy  as  hydrogen,  it  follows  that  hydro- 
chloric acid  is  composed  of  1  part  by  weight  of  hydrogen 
to  35.46  parts  by  weight  of  chlorine.  Its  molecular  weight, 
therefore,  is  1  +  35.46  or  36.46.  The  formula  assigned  to 
it  is  HC1.  It  is  an  example  of  a  very  important  acid  that 
contains  no  oxygen. 

123.  Chlorine  is  irritating  to  the  lining  of  the  nose  and 
throat  and  if  breathed  in  large  quantities  causes  inflamma- 
tion. It  is  2.5  times  heavier  than  air,  and  hence  is  collected 
by  downward  displacement.  Chlorine  is  one  of  the  most 
active  elements  and  is  never  found  in  the  free  state.  It  dis- 
solves in  water,  the  solution  being  known  as  chlorine  water. 


CHLORINE  147 

This  solution  is  frequently  used  as  a  substitute  for  the  gas. 
If  the  solution  is  placed  in  the  sunlight,  oxygen  is  liberated 
and  hydrochloric  acid  is  formed  : 

H20  +  C12  ->-  2  HC1  +  O. 

Chlorine  is  a  powerful  bleaching  agent.  This  property 
probably  depends  upon  the  above  reaction,  the  bleaching 
being  due  to  the  liberated  oxygen,  for  the  chlorine  does  not 
act  upon  colored  fabrics  unless  they  are  moist.  Chlorine 
combines  directly  with  many  metals,  forming  chlorides : 

Cu  +  2  Cl  ->-  CuCl2. 

The  chlorides  may  also  be  formed  by  the  action  of  hydro- 
chloric acid  on  the  metal  or  on  an  oxide  of  the  metal : 

Zn  +  2  HC1  -»-  ZnCl2  +  2  H ; 
CaO  +  2  HC1  -»-  CaCl2  -r  H2O. 

124.  Bleaching  Powder.  Large  quantities  of  chlorine  are 
needed  in  the  bleaching  industries,  but  as  it  is  inconvenient 
to  handle  or  transport  the  free  gas  it  is  stored  in  the  form  of 
bleaching  powder,  sometimes  called  bleach  or  improperly 
chloride  of  lime.  It  is  made  by  passing  chlorine  over  slaked 

Ca(OH)2  +  2  Cl  ->-  CaOCl2  +  H2O. 

The  formula  CaOCl2  is  the  one  usually  given  for  bleach- 
ing powder.  When  needed,  the  chlorine  can  be  again 
obtained  from  the  bleaching  powder  by  treating  it  with 
sulphuric  acid : 

CaOCl2  +  H2S04  -^  2  Cl  +  CaSO4  +  H2O. 

In  addition  to  its  use  in  providing  chlorine  for  bleaching, 
this  powder  is  valuable  as  a  disinfectant.  It  is  slowly  de- 


148  INORGANIC  CHEMISTRY 

composed  by  the  carbon  dioxide  of  the  atmosphere,  and  the 
chlorine  is  liberated  : 

CaOCk  +  CO2  -»-  CaCO3  +  2  Cl. 

The  disinfecting  properties  are  probably  due  to  the  libera- 
tion of  oxygen  produced  by  the  action  of  the  chlorine  on 
water. 

125.  Sodium.  It  is  comparatively  easy,  as  has  been 
shown,  to  determine  that  chlorine  is  one  of  the  elements 
found  in  salt,  but  there  is  no  method  suited  to  the  small 
laboratory  that  will  show  what  else  is  present  in  salt.  If, 
however,  the  salt  is  fused  and  an  electric  current  is  passed 
through  it,  chlorine  will  be  given  off  at  the  positive  pole, 
while  at  the  negative  pole  a  new  substance  will  be  found. 
It  is  a  soft  solid  which  has  a  silver-white  metallic  luster, 
and  becomes  covered  with  a  coating  of  white  material  when 
exposed  to  the  air.  It  is  the  metal  known  as  sodium  (Na). 
If  a  bit  of  sodium  is  warmed  and  placed  in  a  bottle  full 
of  chlorine,  it  burns  with  a  dazzling  yellow  light  and  a  white 
powder  is  formed  which  can  be  identified  as  salt.  Shavings 
of  cold  sodium  thrown  into  a  jar  of  chlorine  are  slowly  con- 
verted into  a  white  mass  of  salt.  Common  salt,  then,  is 
the  compound  formed  by  the  union  of  the  metal  sodium 
and  the  gas  chlorine.  It  is  sodium  chloride  (NaCl)  and  is 
evidently  the  sodium  salt  of  hydrochloric  acid,  for  it  yields 
that  acid  when  acted  upon  by  sulphuric  acid,  the,  equation 

bemg  :         2  NaCl  +  H2SO4  -»-  Na^SC*  -f  2  HO 


Sodium  is  very  active  chemically  and  combines  readily  with 
many  other  elements,  especially  with  chlorine  and  oxygen. 
It  is  kept  in  coal  oil,  as  it  absorbs  oxygen  and  moisture  from 
the  air  and  quickly  tarnishes.  It  decomposes  water  more 


SODIUM  149 

vigorously  than  calcium  does,  liberating  one  half  the  hydro- 
gen and  forming  sodium  hydroxide  : 


The  water  containing  sodium  hydroxide  (NaOH)  has  a  soapy 
feel  when  rubbed  between  the  fingers  and  it  exhibits  the 
property  of  turning  red  litmus  paper  blue  in  a  more  marked 
way  than  does  limewater.  When  burned  in  the  air  sodium 
is  changed  to  sodium  oxide  (2  Na  +  O  ->-  Na^O),  which 
added  to  water  gives  the  hydroxide  : 


126.  Sodium  hydroxide  is  better  known  under  the  name 
of  caustic  soda  or  soda  lye.     It  is  a  white  solid  which  readily 
absorbs  water  and  carbon  dioxide  if  exposed  to  the  air.     It 
has  a  very  corrosive  effect  on  animal  and  vegetable  tissues. 
The  chemically  pure  hydroxide  is  usually  cast  into  sticks. 
Sodium  hydroxide  is  used  in  many  industries,  especially  in 
the  manufacture  of  hard  soaps.     The  material  sold  in  cans 
as  potash  or  lye  is  usually  crude  sodium  hydroxide.     It  is 
sometimes  produced  by  passing  the  electric  current  through 
strong  brine,  a  process  which  causes  hydrogen  and  chlorine 
to  be  given  off  and  which  allows  the  hydroxide  to  remain  in 
solution.     It  is  also  made  by  boiling  sodium  carbonate  with 
milk  of  lime  : 

NasCOs  +  Ca(OH)2  -»-  2  NaOH  +  CaCO3. 

The  solution  of  sodium  hydroxide  is  separated  from  the 
insoluble  calcium  carbonate  and  concentrated  by  heating 
in  iron  kettles. 

127.  Sodium   sulphate    (Na^SC^  •  10  H2O)   is   commonly 
known  as  Glauber's  salt.     It  is  produced  when  sulphuric 


150  INORGANIC  CHEMISTRY 

acid  acts  upon  common  salt  (121).  It  forms  large  crystals 
which  are  efflorescent;  so  the  commercial  article  usually 
contains  some  white  powder.  It  is  used-  in  medicine  and 
in  the  manufacture  of  washing  soda  and  of  glass. 

128.  Sodium  sulphite  (Na^SOa  •  7  H2O)  was  mentioned  in 
Chapter  X.     It  is  prepared  by  the  action  of  sulphur  dioxide 
on  sodium  hydroxide.     The  equation  is 

SO2  +  2  NaOH  ^NasSOs  +  H2O. 

When  treated  with  an  acid,  sodium  sulphite  yields  sulphur 
dioxide  (86). 

129.  Sodium  carbonate  (Na^COs  •  10  H2O)  is  the  substance 
known  as  washing  soda  or  sal  soda.     It  crystallizes  in  large 
crystals  which  are  strongly  efflorescent.     When  the  sulphite 
and  the  carbonate  are  dried  until  most  of  the  water  of 
crystallization  is  driven  off  they  are  said  to  be  anhydrous. 
The  solution  of  sodium  carbonate  is  slightly  alkaline  and 
will  turn  red  litmus  paper  blue.     It  is  used  to  soften  water 
and  to  make  soap,  and  in  the  manufacture  of  glass  and 
many  chemical  reagents. 

130.  Sodium  bicarbonate   (NaHCO3)   or  faking  soda  is 
carbonic  acid  with  only  one  of  the  hydrogen  ?  corns  replaced 
by  sodium.     It  can  be  made  by  passing  carbon  dioxide 
through  a  strong  solution  of  sodium  carbonate ;   or  in  other 
words,  by  the  action  of  carbonic  acid  on  sodium  carbonate. 
The  equation  is : 

NasCOs  +  H2CO3  ->-  2  NaHCO3. 

As  the  bicarbonate  is  much  less  soluble  than  the  carbonate, 
it  settles  out.  When  heated  it  gives  off  carbon  dioxide  and 
water,  and  changes  back  to  the  normal  carbonate  : 

2  NaHCO3  -»-  Na.COs  +  CO2  +  H2O. 


SODIUM 


151 


When  mixed  with  any  acid  material,  such  as  sour  milk  or 
tartaric  acid,  it  gives  off  carbon  dioxide.  This  property 
accounts  for  its  Use  in  cooking,  the  liberated  carbon  dioxide 
being  the  substance  that  makes  bread,  pastry,  or  cake 
light  (427). 

131.  Test  for  Sodium.    To  test  for  sodium  dip  a  platinum 
wire  into  the  substance  to  be  tested  and  place  it  in  the  non- 
luminous  flame  (Fig.  97).     A  deep  yellow  color  given  to 
the  flame  shows  the  pres- 
ence of  sodium.    As  sodium  ^  — rvv 
chloride   is   present    nearly 

everywhere,  precaution 
must  be  taken  to  prevent 
the  accidental  introduction 
of  this  material  when  test- 

FIG.  97. —Flame  test  for  sodium. 

ing  for  sodium. 

132.  Test  for  Hydrochloric  Acid  or  a  Chloride.     Add  to 

the  solution  of  the  substance  a  few  drops  of  the  laboratory 
solution  of  silver  nitrate.  A  white  curdy  precipitate,  or  a 
milkiness,  which  does  not  dissolve  in  nitric  acid,  is  proof  of 
the  presence  of  hydrochloric  acid  or  a  chloride. 


EXERCISES 

Ex.  85.  Tell  what  you  can  about  the  distribution  of  salt  in  nature. 
How  is  salt  prepared  for  use?  To  what  extent  fe  salt  soluble?  Is  it 
any  more  soluble  in  hot  water  than  in  cold?  Is  that  true  of  most 
soluble  solids?  Why  does  ordinary  table  salt  become  moist  in  the 
air  ?  Will  pure  salt  remain  dry  ? 

Ex.  86.  Place  some  salt  in  the  flask  (A)  of  an  apparatus  like  Fig. 
96  and  add  sulphuric  acid.  Gently  warm  and  collect  some  of  the 
gas  by  downward  displacement.  How  does  the  gas  behave  in  contact 
with  the  air?  Cautiously  note  the  odor  of  the  gas.  Will  it  burn  or 
support  combustion?  Is  it  soluble  in  water?  Hold  a  piece  of  moist 


152 


INORGANIC  CHEMISTRY 


blue  litmus  paper  in  the  gas.  What  change  takes  place  ?  Dip  litmus 
paper  in  the  aqueous  solution  of  the  gas.  Compare  this  solution 
with  the  hydrochloric  acid  of  the  laboratory.  What  is  the  composi- 
tion of  the  latter?  Can  you  show  that  hydrochloric  acid  contains 
hydrogen  ?  (122) 

Ex.  87.  Clean  out  the  apparatus  used  in  the  last  experiment  and 
place  some  manganese  dioxide  in  the  flask  (A).  Add  some  strong  hydro- 
chloric acid  and  heat  the  mixture.  Collect  several  portions  of  the 
gas  by  downward  displacement,  allowing  as  little  of  the  gas  as  possible 
to  escape  into  the  room.  What  is  the  color  of  the  gas?  Cautiously 
note  the  odor.  What  is  the  name  of  the  gas  ?  Why  was  it  so  named  ? 
What  was  the  source  of  this  gas  in  the  experiment?  Will  it  dissolve 
in  water?  Place  a  colored  flower  and  a  moist  piece  of  colored  calico 
in  a  bottle  full  of  the  gas.  Will  chlorine  bleach  dry  materials?  To 
what  is  the  bleaching  due  ?  Write  the  reaction  between  chlorine  and 
water.  What  is  formed  by  the  action  of  chlorine  on  a  metal?  In 
what  other  ways  may  chlorides  be  formed?  How  may  it  be  proved 
that  hydrochloric  acid  is  composed  of  hydrogen  and  chlorine?  In 
what  proportions  by  volume  do  the  gases  combine?  In  what  pro- 
portion by  weight  ? 

Ex.  88.  In  a  test  tube  place 
some  bleaching  powder.  Moisten 
with  water  and  add  sulphuric 
acid.  What  gas  is  given  off? 
Write  the  reaction.  Explain 
how  bleaching  powder  is  manu- 
factured. Write  the  reaction.  Of 
what  use  is  bleaching  powder  ? 

Ex.  89.  (Teacher.)  Drop  a 
piece  of  sodium  the  size  of  a  grain 
of  wheat  on  the  surface  of  a  pan 
of  water.  Do  not  stand  too  close 
as  the  sodium  sometimes  explodes. 
Touch  the  sodium  while  on  the 
water  with  a  taper.  Is  an  inflammable  gas  evolved  ?  Wrap  a  similar 
piece  of  sodium  loosely  in  tin  foil  (to  make  it  sink)  and  collect  the  gas 
in  a  test  tube  previously  filled  with  water  as  shown  in  Fig.  98.  Test 
the  gas  with  a  lighted  splint.  Write  the  reaction.  Does  the  sodium 


CHLORINE   AND  SODIUM 


153 


liberate  all  the  hydrogen  of  water?  Is  sodium  chemically  active? 
Why  is  it  kept  in  coal  oil  ?  How  is  it  prepared  from  common  salt  ? 

Ex.  90.  What  compound  remains  when  sodium  acts  upon  water? 
What  effect  does  the  solution  of  sodium  hydroxide  have  on  litmus 
paper?  Compare  with  limewater  and  hydrochloric  acid.  What  is 
the  common  name  for  sodium  hydroxide  ?  For  what  is  it  used  ?  What 
is  the  substance  sold  in  cans  under  the  name  of  potash?  How  is  it 
manufactured  ? 

Ex.  91.  Examine  and  describe  ordinary  washing  soda.  What  is 
its  chemical  name  and  formula  ?  What  is  meant  by  anhydrous  sodium 
carbonate  ?  Dissolve  a  little  washing  soda  in  water  and  test  with  litmus 
paper.  What  is  a  common  use  for  this 
material  ?  Make  a  saturated  solution 
of  sodium  carbonate  and  pass  carbon 
dioxide  through  it.  (See  Fig.  99.) 
What  happens?  What  is  the  compo- 
sition of  the  precipitate?  Write  the 
reaction.  Add  hydrochloric  acid  to 
washing  soda  and  baking  soda.  Re- 
sult? Which  would  yield  the  most 
carbon  dioxide,  a  pound  of  washing 
soda  or  a  pound  of  baking  soda? 
Add  baking  soda  to  sour  milk.  What 
gas  is  given  off  ?  How  can  you  prove 
that  a  gas  is  carbon  dioxide? 

Ex.  92.     Dip  a  platinum  wire  in  a 

solution  of  table  salt  and  place  it  in  the  non-luminous  flame.  What 
happens  ?  Hold  a  piece  of  glass  rod  in  the  flame.  Have  you  any  evi- 
dence that  there  is  sodium  in  the  glass  ?  What  is  the  test  for  sodium  ? 
Test  a  solution  of  common  salt  with  the  laboratory  solution  of  silver 
nitrate.  Is  this  a  general  test  for  chlorides  ?  Ask  the  teacher  to  give 
you  several  substances  and  see  if  you  can  tell  which  are  chlorides. 


FIG.  99. — Passing  carbon  di- 
oxide through  a  solution  of  sodium 
carbonate. 


CHAPTER  XV 
ACIDS,   BASES,   AND   SALTS 

133.  Acids.     When  sulphur  trioxide  was  added  to  water 
(65),  the  solution  had  a  sour  taste  and  turned  blue  litmus 
paper  red.     The  same  thing  was  found  to  be  true  in  a  less 
marked  way  of  sulphur  dioxide  (83)  and  of  carbon  dioxide 
(102) ;    and  the  combinations  made  by  these  oxides  with 
water  were  called  acids.     The  oxides  of  several  other  ele- 
ments behave  in  the  same  way  as  those  of  sulphur  and 
carbon,  and  these  compounds,  known  as  acids,  are  of  great 
importance.     The  acids  mentioned  must,  from  their  method 
of  preparation,  contain  hydrogen,  oxygen,  and  some  other 
element,  but  it  has  been  shown  that  not  all  acids  are  formed 
by  the  union  of  an  oxide  with  water.     A  few  acids,  one  of 
which  is  hydrochloric  acid,  are  formed  by  the  union  of  one 
other  element  with  hydrogen  and  contain  no  oxygen.     All 
acids  contain  hydrogen,  which  may  be  replaced  by  a  metal 
with  the  formation  of  a  saltlike  substance.     Most  acids 
will  decompose  carbonates,  liberating  the  carbon  dioxide 
with  effervescence. 

134.  Bases.     Not  all  oxides  form  acids  when  united  with 
water.     It  has  been  seen  that  when  calcium  oxide  or  sodium 
oxide  unites  with  water  the  compound  formed  has  proper- 
ties quite  different  from  the  acids.     Solutions  of  these  com- 
pounds turn  red  litmus  paper  blue,  have  a  brackish  taste, 
and  do  not  decompose  carbonates.     These  compounds  are 

154 


ACIDS,  BASES,  AND   SALTS  155 

known  as  bases  and  contain  a  metal  combined  with  oxygen 
and  hydrogen. 

135.  Neutralization.     A  solution  of  sodium  hydroxide, 
as  has  been  said,  turns  red  litmus  paper  blue,  and  a  solu- 
tion of  hydrochloric  acid  turns  blue  litmus  paper  red.     If, 
now,  the  hydrochloric  acid  solution  is  carefully  added  to 
the  sodium  hydroxide  and  the  solution  tested  from  time  to 
time  by  placing  a  drop  on  litmus  paper,  a  point  can  be 
found  when  the  solution  does  not  affect  litmus  paper  at  all. 
It  will  turn  neither  the  red  paper  blue  nor  the  blue  paper 
red.     The  solution  has  neither  a  sour  nor  a  brackish  taste. 
In  fact,  all  the  characteristic  properties  of  both  acid  and  base 
have  disappeared,  and  the  two  are  said  to  have  neutralized 
each  other,  the  act  being  known  as  neutralization.     When  an 
acid  and  a  base  neutralize  each  other  the  action  is  quanti- 
tative; that  is,  it  always  takes  exactly  the   same  amount 
of  the  acid  to  neutralize  a  given  quantity  of  the  base.     If 
the  quantity  of  either  acid  or  base  is  known,  the  other  can 
easily  be  calculated. 

136.  Salts.     If  the  solution  resulting  from  neutralizing 
sodium  hydroxide  with  hydrochloric  acid  is  evaporated  to 
dryness,  it  will  be  found  that  the  white  substance  remain- 
ing in  the  dish  is  common  salt  (sodium  chloride).     If  sul- 
phuric acid  is  neutralized  with  sodium  hydroxide,  the  prod- 
uct is  sodium  sulphate  (Glauber's  salt)..    Calcium  hydrox- 
ide and  sulphuric  acid    give  calcium  sulphate   (gypsum). 
These  compounds  are  examples  of  a  class  of  substances 
known  as  salts.     When  any  acid  is  neutralized  by  a  base  one 
of  the  products  formed  is  a  salt;    the  other  product  in  every 
case  is  water.     The  formulas  for  sodium  chloride  (NaCl), 
sodium  sulphate  (Na2SO4),  and  calcium  sulphate  (CaSO4) 
indicate  that  the  formation  of  the  salt  really  consists  in  the 


156  INORGANIC  CHEMISTRY 

replacing  of  the  hydrogen  of  the  acid  by  a  metal,  such  as 
sodium  or  calcium.  The  reaction  for  the  formation  of 
calcium  sulphate  is  typical : 

Ca(OH)2  +  H2SO4  -»-  CaSO4  +  2  H2O. 

It  will  be  seen  that  the  metallic  part  of  the  base  (Ca)  re- 
places the  hydrogen  of  the  acid,  and  this  hydrogen  combines 
with  the  hydrogen  and  oxygen  of  the  base  to  form  water. 

137.  Definitions.     An   acid   is    a    compound    containing 
hydrogen,  which  may  be  replaced  by  a  metal,  the  product 
formed  being  a  salt. 

A  base  is  a  compound  which  contains  hydroxyl  combined 
with  a  metal  (or  a  basic  radical)  and  which,  when  treated 
with  an  acid,  easily  exchanges  its  metal  for  hydrogen. 

A  salt  is  a  compound  formed  when  a  metal  replaces  one  or 
more  of  the  hydrogen  atoms  of  an  acid.  Salts  may  be  formed 
also  by  the  action  of  an  acid  (1)  on  a  metal,  and  (2)  on  an 
oxide : 

(1)  Fe    +  H2SO4 -*- FeSO4  +  H2 ; 

(2)  FeO  +  H2S04  ->•  FeSO4  +  H2O. 

138.  Alkali.     The  bases  or  hydroxides  formed  by  most 
of  the  metals  are  insoluble  in  water.     The  hydroxides  of 
sodium,  potassium,  calcium,  and  a  few  others  are  soluble  in 
water  and  show  in  a  marked  way  the  property  of  producing 
a  blue  color  with  certain  vegetable  dyes.     They  are  also 
caustic  in  their  action.     These  hydroxides  are  called  alka- 
lies.    A  substance  that  turns  litmus  or  other  of  these  vege- 
table dyes  blue  is  said  to  have  an  alkaline  reaction.    A  sub- 
stance that  turns  the  blue  litmus  red  is  said  to  have  an  acid 
reaction,  and  one  that  has  no  effect  on  litmus  is  said  to  be 
neutral.    The  organic  coloring  matter  that  is  used  to  de- 


ACIDS,   BASES,   AND  SALTS  157 

termine  whether  a  substance  is  alkaline,  acid,  or  neutral 
is  called  an  indicator.  Litmus  is  the  most  common  indicator. 
Other  important  indicators  are  solutions  of  phenolphthalein 
and  methyl  orange  —  two  coal  tar  compounds,  and  the 
aqueous  extract  of  the  cochineal  insect. 

139.  Naming  the  Acids,  Salts,  and  Bases.      Those  acids 
which  are  composed  of  only  two  elements  (binary  acids) 
are  given  the  prefix  hydio  and  the  suffix  ic.     The  salts  of 
such  acids  have  the  suffix  ide,  and  the  prefix  hydro  is  dropped ; 
thus : 

Hydrochloric  acid  (HC1).    Sodium  chloride  (NaCl). 
Most  acids  contain  three  elements — hydrogen,  oxygen,  and 
one  other  element — and  are  known  as  ternary  acids.     Such 
acids  are  given  the  ending  ic,  no  prefix  being  used,  and  the 
salt  is  given  the  ending  ate : 

Sulphuric  acid  (H2SO4).    Calcium  sulphate  (CaSO4). 

In  case  an  element  forms  more  than  one  acid  containing 
oxygen,  the  one  containing  the  larger  percentage  of  oxygen 
is  given  the  ending  ic  and  the  other  the  suffix  ous.  The 
salt  in  this  latter  case  has  the  ending  ite  : 

Sulphurous  acid  (H2SO3).     Sodium  sulphite  (Na2SO3). 
All  the  bases  are  called  hydroxides,  the  name  of  the  metal  or 
basic  radical  being  prefixed ;  for  example,  potassium  hydrox- 
ide (KOH). 

140.  Normal,  Acid,  and  Basic  Salts.     Some  of  the  acids, 
as  sulphuric  acid  (H2SO4)  and  carbonic  acid  (H2CO3),  con- 
tain two  atoms  of  hydrogen  in  the  molecule.     Sodium  has 
a  univalent  atom  which  has  the   power  of  replacing  only 
one  hydrogen  atom.     It  is  possible  to  bring  about  a  com- 
bination in  which  only  one  hydrogen  atom  of  the  acid  is 


158  INORGANIC  CHEMISTRY 

replaced,  as  for  instance,  NaHSO4,  in  which  half  the  hydro- 
gen in  sulphuric  acid  is  replaced  by  sodium.  Such  a  salt 
is  known  as  an  acid  salt  because  it  contains  hydrogen,  the 
characteristic  constituent  of  acids.  The  salt  in  which  all 
the  hydrogen  is  replaced  is  a  normal  salt.  For  example, 
NaHS04  is  acid  sodium  sulphate,  sometimes  called  sodium 
hydrogen  sulphate;  and  Na2SO4  is  normal  sodium  sul- 
phate. Baking  soda,  or  sodium  bicarbonate,  NaHCO3,  is 
another  example  of  an  acid  salt.  The  acid  salts,  when 
treated  with  a  base,  are  converted  into  normal  salts  ;  and 
it  has  been  shown  that  normal  salts  can  be  changed  to  the 
acid  salts  by  the  action  of  an  acid  : 

NaHSO4  +  NaOH  -»-  Na2SO4  +  H2O; 
H2SO4  ->-  2  NaHSO4. 


(See  also  sodium  bicarbonate  and  calcium  bicarbonate.) 
The  acids  which  have  only  one  hydrogen  atom  in  the  mole- 
cule obviously  cannot  form  acid  salts.  There  are  also  a 
few  salts  in  which  the  base  is  not  completely  neutralized 
by  the  acid.  Such  salts  are  known  as  basic  salts. 

141.  Non-metals  and  Metals.  It  has  been  seen  that 
certain  elements  form  oxides  which  unite  with  water  to  pro- 
duce acids,  while  the  oxides  of  other  elements  form  bases 
with  water.  The  base-forming  elements  are  for  the  most 
part  metals  (sodium,  iron,  zinc,  copper).  The  acid  form- 
ing elements,  with  a  few  exceptions,  have  no  metallic  prop- 
erties. It  is  customary  for  the  sake  of  convenience  in  dis- 
cussion to  divide  the  elements  into  two  classes  —  non- 
metals  and  metals.  Those  elements  that  have  at  least  one 
oxide  that  unites  with  water  to  form  an  acid  are  classified 
as  non-metals.  Those  elements  whose  oxides  form  bases 
are  known  as  metals.  Unfortunately  for  the  simplicity  of 


ACIDS,   BASES,   AND   SALTS  159 

this  classification  there  are  "  border  line  "  elements  that 
are  sometimes  acidic  and  sometimes  basic. 

Note.  An  oxide  which  forms  an  acid  when  added  to  water  is  called 
an  anhydride.  Sulphur  trioxide  is  sulphuric  anhydride ;  that  is,  it  is 
the  oxide  which  forms  sulphuric  acid  when  added  to  water.  Formerly 
the  anhydrides  were  called  acids,  and  even  at  the  present  time  confu- 
sion is  sometimes  caused  by  the  fact  that  in  trade  certain  anhydrides 
are  listed  as  acids. 

The  following  elements  are  selected  for  discussion  in  this 
text: 

NON-METALS,  OB  ACID-FORMING  ELEMENTS       METALS,  OB  BASE-FOBMINQ  ELEMENTS 

Hydrogen  Sodium 

Oxygen  Potassium 

Nitrogen  Calcium 

Sulphur  Magnesium 

Carbon  Copper 

Chlorine  Silver 

Phosphorus  Zinc 

Silicon  Aluminum  , 

Arsenic  Lead 

Boron  Iron 

Six  of  the  non-metals  and  two  of  the  metals  have  already 
been  discussed.  The  remaining  non-metals  will  next  be 
considered,  and  afterward  the  metals  and  their  salts. 

Hydrogen  really  belongs  in  a  class  by  itself  but  for  con- 
venience it  is  usually  classed  as  a  non-metal. 

EXERCISES 

Ex.  93.  Dissolve  about  two  grams  of  sodium  hydroxide  in  100 
cubic  centimeters  of  water.  Add  5  cubic  centimeters  of  hydrochloric 
acid  to  100  cubic  centimeters  of  water.  Test  both  solutions  with  red 
and  blue  litmus  paper.  Now  carefully  add  the  acid  solution  to  the 


160  INORGANIC   CHEMISTRY 

sodium  hydroxide  solution  until  the  mixture  will  not  change  the  color 
of  either  the  red  or  the  blue  paper.  Evaporate  the  mixture  to  dryness 
and  determine  whether  the  residue  is  common  salt.  What  are  the 
characteristics  of  the  acids?  What  element  do  they  all  have  in  com- 
mon? What  is  the  characteristic  group  of  the  bases?  How  do  bases 
and  acids  act  on  one  another?  What  is  meant  by  neutralization? 
When  an  acid  neutralizes  a  base  what  is  formed?  How  should  you  de- 
fine an  acid  ?  A  base  ?  A  salt  ?  Mention  three  methods  of  forming 
salts. 

Ex.  94.  What  is  meant  by  an  alkali?  By  alkaline  reaction?  By 
acid  reaction?  When  is  a  substance  said  to  be  neutral?  What  is  an 
indicator?  Try  weak  solutions  of  sodium  hydroxide  and  hydrochloric 
acid  with  phenolphthalein  indicator ;  with  cochineal  indicator ;  with 
methyl  orange.  Record  the  changes  in  color  in  each  case.  If  red 
cabbage  is  available  express  some  of  the  juice  and  determine  whether 
it  could  be  used  as  an  indicator.  Make  a  list  of  any  substances  at  home 
that  are  acid  or  alkaline  in  reaction.  What  is  the  reaction  of  your  per- 
spiration ?  Of  your  saliva  ? 

Ex.  95.  What  is  meant  by  a  binary  acid?  How  are  these  acids 
named  ?  Give  an  example.  When  an  element  forms  two  acids  how 
are  they  named?  How  are  the  salts  named?  How  are  the  bases 
named  ?  What  is  meant  by  an  acid  salt  ?  Give  an  example.  What 
is  meant  by  an  anhydride  ?  Of  the  elements  studied  which  are  metals 
and  which  non-metals? 


CHAPTER   XVI 
NITRIC  ACID   AND    OXIDES   OF   NITROGEN 

142.  Chile  Saltpeter.  In  northern  Chile  there  are  great 
beds  of  the  substance  commonly  known  as  Chile  saltpeter, 
or  nitrate  of  soda.  When  pure,  this  material  forms  trans- 
parent, colorless  crystals  which  are  very  soluble  in  water. 


FIG.  100.  —  Mining  nitrate  of  soda  or  Chile  Saltpeter. 

In  nature  it  is  mixed  with  common  salt  and  earth,  from 
which  it  is  separated  by  being  dissolved  in  boiling  water 
and  then  allowed  to  crystallize  as  the  water  cools.  Nearly 
two  million  tons  of  nitrate  of  soda  are  exported  from  Chile 
each  year.  The  larger  part  of  this  is  used  as  a  fertilizer;  the 
remainder  is  utilized  in  the  manufacture  of  nitric  acid.  If 
EV.  CHEM.  — 11  161 


162 


INORGANIC  CHEMISTRY 


a  particle  of  Chile  saltpeter  is  placed  in  the  flame  of  a  Bunsen 
burner  or  an  alcohol  lamp  the  flame  will  be  colored  an  in- 
tense yellow.  This  fact  shows  that  this  substance  is  a  com- 
pound of  sodium  (131).  It  is  evidently  a  salt,  but  since 
Chile  saltpeter  will  not  give  the  test  for  any  of  these  acids 
(88,  101,  and  132),  the  acid  with  which  the  sodium  is  com- 
bined is  evidently  different  from  any  previously  described. 
If  Chile  saltpeter  is  mixed  with  about  its  own  weight  of  sul- 
phuric acid  and  the  mixture  is  gently  warmed,  a  vapor  es- 
capes which,  when  condensed  to  a  liquid,  proves  to  be  nitric 
acid,  to  which  the  formula  HNO3  has  been  assigned.  Chile 
saltpeter,  then,  is  the  sodium  salt  of  nitric  acid ;  that  is,  it 
is  sodium  nitrate  (NaNOs). 

143.  Nitric  acid  is  prepared  commercially  by  heating 
sodium  nitrate  with  sulphuric  acid,  upon  which  the  follow- 
ing reaction  takes  place: 

2  NaNO3  +  H2SO4  -*•  Na2SO4  +  2  HNO3. 

The  apparatus  in  Fig.  101  is  adapted  to  the  preparation  of 
the  acid  on  a  small  scale.  A  is  a  small  glass  retort  in  which 

are  placed  25  grams  of  sodium 
nitrate.  About  15  cc.  of  sul- 
phuric acid  are  added  and  the 
mixture  is  gently  heated.  The 
nitric  acid  distills  over  and  is 
condensed  in  the  test  tube  B, 
which  is  surrounded  by  cold 
water,  preferably  ice  water. 

Pure  nitric  acid  is  a  color- 
less liquid  about  one  and  one 

half  times  as  heavy  as  water.  It  gives  off  colorless  fumes 
when  exposed  to  the  air.  The  concentrated  nitric  acid  of 


FIG.  101. — Apparatus  used  in  mak- 
ing nitric  acid. 


NITRIC  ACID  163 

the  laboratory  contains  68  per  cent  of  HNO3,  the  rest  being 
water.  In  the  above  experiment  the  acid  is  slightly  colored 
because,  when  nitric  acid  is  boiled,  a  small  part  of  it  is  de- 
composed according  to  the  following  equation  : 

2  HNO3  -^  H2O  +  2  NO2  +  O. 

Nitrogen  peroxide,  NC>2,  is  a  reddish  brown  gas  which  dis- 
solves in  the  undecomposed  nitric  acid  and  colors  it.  The 
same  decomposition  takes  place  when  nitric  acid  is  exposed 
to  strong  light,  and  in  consequence,  the  bottles  in  which 
concentrated  nitric  acid  is  stored  often  contain  a  reddish 
brown  gas  above  the  liquid,  which  is  itself  somewhat  colored. 

Strong  nitric  acid  acts  violently  on  many  substances, 
especially  those  of  animal  and  vegetable  origin.  It  causes 
painful  wounds  when  it  comes  in  contact  with  the  flesh, 
it  eats  through  clothing,  it  burns  wood  and  dissolves  metals, 
and  is,  in  fact,  one  of  the  most  active  of  chemical  substances. 
Even  the  dilute  acid  stains  the  skin  and  clothing  yellow,  and 
the  stain  cannot  be  removed.  The  greatest  care  should 
be  exercised  in  working  with  nitric  acid. 

In  dilute  solutions,  nitric  acid  has  many  of  the  character- 
istics of  the  other  acids  that  have  been  studied.  It  has  a 
decidedly  sour  taste,  and  it  turns  blue  litmus  paper  red.  It 
reacts  with  oxides,  hydroxides,  and  carbonates  to  form  salts, 
as,  for  example : 

CuO  +  2  HNO3  ->-  H2O  +  Cu(NO3)2  (copper  nitrate) ; 
NaOH  +  HNO3  -»-  H2O  +  NaNO3  (sodium  nitrate) ; 
CaCO3  +  2  HNO3  ->-  H2O  +  CO2  +  Ca(NO3)2    (calcium  ni- 
trate). 

When  nitric  acid  acts  on  a  metal,  a  salt  is  formed  as  would 
be  expected,  but  no  hydrogen  is  liberated;  in  this  respect 


164  INORGANIC   CHEMISTRY 

it  differs  from  sulphuric  and  hydrochloric  acids.  Instead 
of  hydrogen  a  gas  which  is  one  of  the  oxides  of  nitrogen  is 
given  off.  The  reaction  with  copper  is  usually  written  thus  : 

3  Cu  +  8  HN03  ->•  3  Cu(NO3)2  +  4  H2O  +  2  NO. 
To  explain  this  action  of  nitric  acid  on  metals  it  will  be 
necessary  to  call  attention  to  another  property  of  nitric  acid. 
144.  Nitric  Acid  an  Oxidizing  Agent.  It  was  stated  in 
Chapter  VI  that  it  is  very  difficult  to  make  nitrogen  combine 
with  oxygen  and  hydrogen.  It  is  also  true  that  when  this 
combination  is  brought  about  as  in  nitric  acid  the  compound 
formed  is  very  unstable.  The  formula  for  nitric  acid  (HN03) 
shows  that  it  contains  £f,  or  over  three  fourths,  of  its  own 
weight  of  oxygen.  This  oxygen  is  loosely  held  in  the  mole- 
cule and  is  freely  given  off  to  any  readily  oxidizable  sub- 
stance. This  explains  the  action  of  strong  nitric  acid  on 
animal  and  vegetable  matter ;  for  the  changes  caused  in 
such  materials  by  nitric  acid  are  due  to  oxidation.  Indeed, 
so  readily  does  nitric  acid  give  up  its  oxygen,  that  a  piece 
of  burning  charcoal  thrust  beneath  the  surface  of  the  strong 
acid  will  continue  to  burn,  all  the  oxygen  for  the  combus- 
tion being  obtained  from  the  acid. 

When  nitric  acid  acts  on  a  metal,  it  is  supposed  that 
hydrogen  is  first  liberated,  as  it  is  with  other  acids,  but  that 
the  hydrogen  is  immediately  oxidized  to  water  by  another 
portion  of  nitric  acid  which  gives  up  part  of  its  oxygen  for 
that  purpose.  The  first  part  of  this  reaction  in  the  case  of 
copper  may  be  written  as  follows  : 

3  Cu  +  6  HNO3  ->-  3  Cu(NO3)2  +  6  H. 
The  hydrogen  thus  evolved  would  then  react  with  two  more 
molecules  of  nitric  acid,  thus  : 

6  H  +  2  HNO3  -^  4  H2O  +  2  NO. 


NITRIC  ACID  165 

It  will  be  seen  that  these  two  steps  may  be  combined  into 
the  equation  given  in  the  preceding  section. 

145.  Uses  of  Nitric  Acid.     Over  100,000  tons  of  nitric 
acid  are  used  annually  in  the  industries.  It  is  used  in  the 
manufacture  of  nitroglycerin,    which  is  the  explosive  con- 
stituent of  dynamite.     It  is  used  also  in  making  gun  cotton, 
another  explosive.     It  is  required  in  the  production  of  sul- 
phuric acid  by  the  chamber  process  (84)  as  well  as  in  the 
manufacture  of  dyestuffs.     The  dilute  acid  is  used  in  the 
refining  of  gold  and  silver  and  in  the  preparation  of  the 
copper  plates  from  which  etchings  are  printed. 

146.  Aqua  Regia.     A  mixture  of  nitric  and  hydrochloric 
acid  is  called  aqua  regia.     This  expression  means  "  royal 
water  "  and  it  was  so  named  because  it  is  the  only  acid  that 
will  dissolve  the  "  noble  metals,"  namely,  gold  and  plati- 
num.    Its  action  depends  upon  the  fact  that  the  nitric  acid 
oxidizes  the  hydrogen  of  the  hydrochloric  acid  to  water,  and 
chlorine    is    liberated.     The    chlorine    converts    the    metal 
into   the   chloride,   which   is   soluble.      In   olden   times   all 
liquids  were  considered  to  be  kinds  of  water.     Nitric  acid 
was  called  aqua  fortis,  or  "  strong  water." 

147.  Nitrates.     Nitric  acid  is  monobasic;    that  is,  the 
molecule  contains  one  hydrogen  atom.     It  forms  salts  with 
all  the  metals*     All  the  nitrates  are  soluble  in  water.     Most 
of  them  are  colorless ;   copper  nitrate,  however,  is  blue  and 
nickel  nitrate  is  green.     The  nitrates  are  decomposed  by 
heat.     As  a  general  rule  the  metal  remains  as  the  oxide 
while  oxygen  and  an  oxide  of  nitrogen  are  evolved,  thus : 

Cu(NO3)2  -*•  CuO  +  2  NO2  +  O. 

In  a  few  cases  oxygen  only  is  given  off  when  the  nitrate  is 
heated,  as  for  instance,  in  the  case  of  sodium  nitrate : 
NaNO3  ->•  NaN02  +  O. 


166 


INORGANIC  CHEMISTRY 


Owing  to  the  ease  with  which  they  part  with  their  oxygen, 
the  nitrates,  like  the  acid  from  which  they  are  made,  are 
good  oxidizing  agents. 

148.  Formation   of   Nitric   Acid  from  the   Air.     Nearly 
all  the  nitric  acid  of  commerce  is  manufactured  from  Chile 
saltpeter ;  but  a  small  amount  is  now  made  by  bringing  about 
a  direct  combination  of  the  nitrogen  and  the  oxygen  of  the 
atmosphere.     This  is  effected  by  means  of  powerful  electric 
currents  and  is  profitable  only  where  water  power  makes 
very  cheap  electrical  energy  possible.     At  the  present  time 
the  method  is  used  to  a  limited  extent  in  Norway.     Most 
of  the  nitric  acid  so  produced  is  treated  with  lime  to  form 
calcium  nitrate,  Ca(NO3)2,  which  is  used  as  a  fertilizer. 

149.  Test  for  Nitric  Acid  and  Nitrates.     To  test  for  nitric 
acid  or  nitrates,  dissolve  the  substance  in  water,  place  it  in 

a  test  tube,  and  add  a  small  quantity  of  a 
solution  of  copperas  (ferrous  sulphate). 
The  tube  is  now  inclined  and  some  sul- 
phuric acid  is  poured  slowly  down  the 
side  of  the  tube.  The  sulphuric  acid, 
being  heavier  than  the  other  liquids,  will 
sink  to  the  bottom  of  the  tube  without 
immediately  mixing  with  the  solution. 
If  the  substance  being  tested  contains 
nitric  acid  or  a  nitrate,  a  dark  ring 
(Fig.  102)  will  form  at  the  point  of  con- 
tact between  the  sulphuric  acid  and  the 
solution  above  it. 

150.  Nitrites  and  Nitrous  Acid.     It  was  shown  in  Sec. 
147  that  when  sodium  nitrate  is  strongly  heated  one  third 
of  its  oxygen  escapes  and  the  compound  NaNO2  is  formed. 
This  compound  is  sodium  nitrite.     It  is  more  commonly 


FIG.  102.  — Testing 
for  the  presence  of 
nitric  acid. 


NITRIC  ACID  167 

prepared  by  melting  sodium  nitrate  with  lead.  The  lead 
extracts  one  third  of  the  oxygen  from  the  nitrate  to  form 
lead  oxide,  and  sodium  nitrite  results,  thus : 

NaNO3  +  Pb  ->-  NaNO2  +  PbO. 

The  nitrite  may  be  dissolved  in  water,  leaving  behind  the 
lead  oxide,  which  is  insoluble.  Sodium  nitrite  is  evidently 
the  salt  of  an  acid  having  the  formula  HNO2,  which  should 
be  named  nitrous  acid.  This  acid  has  never  been  prepared 
because  it  is  so  unstable  that  when  it  is  liberated  from  its 
salts  it  immediately  decomposes  into  various  oxides  of  ni- 
trogen. Most  of  the  metals  can  be  made  to  form  nitrites,  but 
none  of  them  are  of  commercial  importance  except  sodium 
nitrite,  which  is  used  in  the  manufacture  of  dyes.  It  is  a 
solid  that  forms  pale  yellow  crystals  and  is  very  soluble  in 
water.  The  nitrates  can  be  reduced  to  nitrites  as  noted 
above  in  the  case  of  sodium  nitrate.  Likewise  the  nitrites 
can  be  easily  oxidized  to  nitrates 

NaNO2  +  O  -»-  NaNO3. 

This  reaction  is  of  interest  because  nitrites  are  undoubtedly 
formed  as  intermediate  compounds  during  the  production 
of  nitrates  in  nature,  as  will  be  shown  in  the  next  chapter. 

151.  Oxides  of  Nitrogen.  Nitrogen  forms  five  different 
combinations  with  oxygen.  These  five  oxides  of  nitrogen 
are  as  follows : 

Nitrous  oxide  N2O 

Nitric  oxide NO  or  N202 

Nitrogen  trioxide N20s 

Nitrogen  peroxide   NO2  or  N2O* 

Nitrogen  pentoxide N2O5 


168  INORGANIC  CHEMISTRY 

These  oxides  furnish  one  of  the  best  examples  of  the  law  of 
multiple  proportions. 

152.  Nitrous  Oxide.     Nitrous  oxide  (N2O)  is  a  colorless 
gas  with  a  slightly 'sweetish  taste.     When  inhaled  it  causes 
a  slight  intoxication  which  shows  itself  in  the  form  of  hys- 
terical   laughing..    For   this  reason    Sir    Humphry    Davy 
named  it  "laughing  gas."     Inhaled  in  larger  quantities,  it 
causes  unconsciousness  and  is,   therefore,  used  in  certain 
minor  surgical  operations,  particularly  in  extracting  teeth. 
For  this  purpose  it  is  condensed  to  a  liquid  and  stored  in 
steel  cylinders.     It  is  prepared  by  heating  ammonium  ni- 
trate (NH4NO3),  a  substance  which  will  be  discussed  in  the 
next  chapter.     The  equation  is  as  follows : 

NH4NO3  ->-  N20  +  2  H2O. 

153.  Nitric  Oxide  and  Nitrogen  Peroxide.    Nitric  oxide 
(NO),  as  has  been  stated,  is  formed  when  nitric  acid  acts 
on  some  metals,  as  zinc  or  copper  (143,  144).    It  is  a  colorless 
gas    that    is    somewhat    poisonous.     Its    most    remarkable 
property  is  its  power  to  combine  directly  with  oxygen  when 
the  two  are  brought  together.     The  reaction  may  be  repre- 
sented thus : 

NO  +  O  ->•  NO2. 

The  product  of  this  reaction  is  nitrogen  peroxide  (NO2), 
which  is  a  gas  that  has  a  reddish  brown  color  and  a  disagree- 
able smell.  It  is  very  poisonous.  If  dilute  nitric  acid  is 
poured  upon  some  pieces  of  zinc  or  copper  in  a  flask,  the 
upper  part  of  the  vessel  is  filled  with  the  colorless  nitric 
oxide  gas  which,  as  it  escapes  into  the  air,  takes  up  oxygen 
and  changes  to  the  reddish  brown  nitrogen  peroxide.  The 
latter  will  give  up  one  half  of  its  oxygen  to  any  readily  oxi- 


OXIDES  OF  NITROGEN 


169 


dizable  substance  and  change  back  to  the  colorless  nitric 
oxide.  This  power  of  the  oxides  of  nitrogen  to  absorb 
oxygen  from  the  atmosphere  and  transfer  it  to  another 
substance  is  utilized  in  the  manufacture  of  sulphuric  acid 
by  the  chamber  process  (84). 


EXERCISES 

Ex.96.  Examine  crystals  of  sodium"  nitrate  (Chile  saltpeter).  Has 
the  substance  the  appearance  of  a  salt?  Test  it  in  the  flame.  What 
metal  is  present?  What  is  the  source  of  the  sodium  nitrate  of  com- 
merce ?  How  is  it  purified  ?  For  what  is  it  used  ? 

Ex.  97.  In  an  apparatus  as  shown  in  Fig.  103  place  a  tablespoonful 
of  sodium  nitrate  and  sufficient  sulphuric  acid  to  cover  the  crystals. 
The  bottle  (C)  should  be  filled 
with  cold  water  or  ice.  Heat 
gently  and  examine  the  liquid 
that  distills.  Compare  with  the 
nitric  acid  of  the  laboratory.  Is 
pure  nitric  acid  colored?  Why 
is  the  acid  colored  in  this  experi- 
ment ?  Why  does  nitric  acid  be- 
come colored  when  exposed  to 
light  ?  Write  the  reaction  for  the 
change.  Dip  a  splinter  of  wood 

and  a  feather  in  nitric  acid.  How  does  nitric  acid  act  on  animal 
and  vegetable  tissues  ?  On  metals  ?  How  does  its  weak  solution  com- 
pare with  solutions  of  other  acids?  How  does  it  act  on  oxides?  Hy- 
droxides ?  Carbonates  ?  Write  the  reactions. 

Ex.  98.  Heat  nitric  acid  in  a  test  tube  with  a  piece  of  zinc  or  copper. 
Describe  the  result.  What  is  the  colored  gas  that  is  formed  ?  Explain 
with  equations  the  action  of  nitric  acid  on  metals.  Why  is  nitric  acid 
said  to  be  a  good  oxidizing  agent  ?  What  uses  are  made  of  nitric  acid  ? 
What  is  the  mixture  of  nitric  and  hydrochloric  acids  called?  What 
effect  does  it  have  on  gold  and  platinum?  What  acid  was  formerly 
called  aqua  fortis?  How  is  nitric  acid  made  commercially?  Can 
nitric  acid  be  made  from  the  nitrogen  of  the  air  ?  Where  is  this  done  ? 


FIG.   103. — Laboratory   apparatus  for 
making  nitric  acid. 


170 


INORGANIC  CHEMISTRY 


Ex.  99.     Heat  a  nitrate  in  a  hard  glass  test  tube  and  prove  that 

oxygen  is  evolved.     Are  the  nitrates  oxidizing  agents?     How  can  you 

test  for  the  presence  of  a  nitrate  ?    Try  the  test  with  a  little  Chile 

saltpeter. 

Ex.  100.     Heat  sodium   nitrate  with  lead.     What  compounds  are 

formed  ?     Write  the  reaction.     What  is  the   formula  of  nitrous  acid  ? 

Has  it  ever  been  prepared  in  the  pure  state  ?     Why  ?     What  change 

takes  place  in  the  nitrites  when  oxidized  ? 

Ex.  101.     In  a  test  tube  heat  a  teaspoonful  of  ammonium  nitrate. 

What  is  the  gas  which  is  given  off?      Give  the  formula.      For  what 

purposes  is  this  gas  used  ?     Why  is   it 
called  "  laughing  gas  "  ? 

Ex.  102.  Fit  a  test  tube  with  a  cork 
in  which  is  fitted  a  small  piece  of  glass 
tubing  (Fig.  104).  Place  a  little  nitric 
acid  and  a  piece  of  zinc  in  the  test  tube. 
Insert  a  cork  and  warm  the  acid.  Is  a 
gas  evolved  ?  What  is  the  color  of  the 
gas  in  the  test  tube?  What  change 
takes  place  when  it  comes  into  contact 

FIG.  104. -Showing  the  forma-     ^    the  air?    Explain;   give  reaction, 
tion  of  NO2.  In    what    commercial    process    is    this 

property  of  nitric  oxide  useful  ?      How 

many  oxides  of  nitrogen  are  known  ?     Give  the  names  and  the  formu- 
las.    How  do  they  illustrate  the  law  of  multiple  proportion  ? 


CHAPTER  XVII 


AMMONIA  AND   ITS   COMPOUNDS 

154.  Ammonia  Water.     One  of  the  most  familiar  sub- 
stances is  the  liquid  so  much  used  in  the  household  under  the 
name   of   ammonia   water   or   spirits    of    hartshorn.     This 
material  (also   called  "  aqua  am- 
monia ")    consists    of   a    gas  dis- 
solved in  water,  which  like  most 

other  dissolved  gases  is  almost 
completely  driven  off  when  the 
solution  is  heated.  The  gas  may 
be  prepared  for  examination  in 
the  apparatus  shown  in  Fig  105. 
The  ammonia  water  is  gently 
warmed  in  the  flask  A  and,  as 
some  water  may  escape  with  the 
gas,  it  is  passed  through  the  tube 
B,  which  contains  lumps  of  lime  to 
absorb  the  water.  As  the  gas  is 
very  soluble  in  water  and  is  lighter 
than  air,  it  is  usually  collected  by 
upward  displacement. 

155.  Ammonia.     The  gas  prepared  in  the  above  experi- 
ment is  ammonia  and  is  a  compound  having  the  formula 
NH3.     It  is  colorless  and  has  an  exceedingly  pungent  and 
penetrating  odor.     When  inhaled  it  brings  tears  to  the  eyes, 
and  in  large  quantities  it  may  cause  suffocation.     It  is 

171 


FIG.  K)5.  —  The  production  of 

ammonia. 


172 


INORGANIC   CHEMISTRY 


about  half  as  heavy  as  air  and  is  very  soluble  in  water, 
one  volume  of  water  dissolving  700  volumes  of  ammonia 
gas  at  ordinary  temperatures.  Ammonia  is  easily  condensed 
to  a  liquid  by  pressure  and  cold.  It  will  not  burn  in  the 
air,  nor  will  it  support  the  combustion  of  a  blazing  stick; 
but  in  oxygen  or  in  heated  air  it  burns  with  a  yellowish 
flame.  A  piece  of  moist  red  litmus  paper  is  changed  to 
blue  if  placed  in  ammonia  gas. 

156.  Ammonia  from  Organic  Matter.  Whenever  any 
animal  or  vegetable  substance  containing  nitrogen  is  heated 
in  a  closed  vessel  so  that  the  air  does  not  have  access  to  it, 

the  nitrogen  passes  out  of  the 
compound  as  ammonia.  This  may 
be  shown  by  heating  bits  of  lean 
meat,  horn,  hoof,  hair,  peas,  or 
beans  in  a  hard  glass  test  tube, 
as  illustrated  in  Fig.  106.  The 
escape  of  ammonia  from  the  tube 
may  be  detected  by  the  odor  or 
by  holding  a  piece  of  moist  red 
litmus  paper  in  the  escaping  gas. 
Ammonia  was  formerly  made  by 
the  destructive  distillation  of  the 
horns  of  the  deer  or  hart  and  for 
FIG.  106.— The  production  of  that  reason  was  termed  spirits  of 

ammonia  from  organic  matter.  .    . 

hartshorn.      Large    quantities    or 

ammonia  are  now  produced  as  a  by-product  in  the  manu- 
facture of  animal  charcoal  from  dried  blood  or  bones.  It 
should  be  noted  that  the  nitrogen  is  not  present  in  the 
animal  or  vegetable  matter  as  ammonia,  but  the  ammonia 
is  formed  during  the  decomposition  of  the  organic  matter 
which  is  brought  about  by  the  heat.  When  animal  or 


AMMONIA  AND  ITS  COMPOUNDS  173 

vegetable  matter  decays,  the  nitrogen  present  is  liberated 
in  combination  with  hydrogen  as  ammonia,  and,  conse- 
quently, the  odor  of  ammonia  is  commonly  noticed  in  stables, 
and  in  the  vicinity  of  cesspools  and  manure  piles. 

157.  Composition  of  Ammonia.     It  is  very  difficult  to 
make  nitrogen   and   hydrogen   unite  directly,  although  it 
can  be  done  to  a  limited  extent  by  passing  electric  sparks 
through  a  mixture  of  the  two  gases.     Experiments  with 
this  method  of  production  show  that  one  volume  of  nitro- 
gen always  combines  with  three  volumes  of  hydrogen,  and, 
as  nitrogen  is  fourteen  times  as  heavy  as  hydrogen,  the  pro- 
portion by  weight  is  14  parts  of  nitrogen  to  3  parts  of  hy- 
drogen. 

158.  Manufacture  of  Ammonia.     Bituminous  coal  con- 
tains small  quantities  of  nitrogen  (one  to  two  per  cent)  and 
some  hydrogen.     When  the  coal  is  heated  in  the  manufac- 
ture of  illuminating  gas,  part  of  the  nitrogen  combines  with 
hydrogen  to  form  ammonia,  which  passes  off  with  the  gas. 
The  illuminating  gas  is  "  washed  "  by  being  made  to  bubble 
through  water,   and  the  ammonia  dissolves   and  remains 
behind   in  the   so-called   ammoniacal   liquor.     This   liquor 
is  then  boiled  with  lime,  and  the  ammonia  is  driven  off  and 
dissolved  in  pure  water,  forming  the  ammonia   water    of 
commerce.     This  is  the  most  common  method  of  manu- 
facturing ammonia;    and  most  of  the  household  ammonia 
comes  from  this  source. 

159.  Ammonia  Combines  with  Water.     When  ammonia 
is  absorbed  by  water,  it  is  believed  that  the  act  is  not  one 
of  mere  solution,  but  that  a  chemical  combination  takes 
place  between  the  ammonia  and  the  water,  thus : 

NH3  +  H2O  -*-  NH4OH. 


174  INORGANIC   CHEMISTRY 

The  compound  NH4OH  is  named  ammonium  hydroxide, 
and  the  chemist  regards  ammonia  water  as  a  solution  of 
ammonium  hydroxide.  This  compound  has  never  been 
separated  because  it  is  so  unstable  that  any  attempt  to  con- 
centrate it  and  free  it  from  water  causes  it  to  decompose 
into  ammonia  and  water,  thus  : 

NH4OH  -*-  NH3  +  H2O. 

This  decomposition  takes  place  at  ordinary  temperatures, 
and  the  odor  of  the  solution  is  due  to  the  escaping  ammonia 
gas.  Ammonia  water  may  contain  as  high  as  35  per  cent 
by  weight  of  ammonia  gas,  which,  as  has  been  shown,  can 
be  driven  off  by  heat.  A  solution  of  this  strength  is  lighter 
than  water,  the  specific  gravity  being  about  0.9.  The  solu- 
tion ordinarily  sold  as  household  ammonia  usually  contains 
not  more  than  10  per  cent  of  the  gas. 

Ammonia  water  is  a  strong  alkali.  It  turns  red  litmus 
paper  blue,  and  when  rubbed  between  the  finger  and  thumb 
has  a  slippery  feel  much  like  a  weak  solution  of  caustic 
soda.  It  is  said  to  be  a  volatile  alkali  because  it  com- 
pletely evaporates  without  leaving  a  residue;  in  which  re- 
spect it  differs  from  caustic  soda,  which  is  sometimes  called 
a  "  fixed  alkali."  The  fact  that  it  leaves  no  residue  gives 
ammonia  water  an  advantage  over  the  fixed  alkalies  for  use 
in  cleaning  glassware  and  clothing.  It  is  used  also  to  soften 
water  in  the  household  and  for  other  purposes  where  a  milder 
alkali  than  caustic  soda  is  required. 

160.  Ammonia  Water  Neutralizes  Acids.  If  aqua  am- 
monia is  slowly  added  to  a  solution  of  hydrochloric  acid,  a 
point  may  be  reached  when  the  solution  is  neutral  and 
has  no  effect  upon  litmus  paper.  If,  now,  this  solution  is 
evaporated  to  dryness,  a  white  substance  remains  in  the 


AMMONIA  AND  ITS  COMPOUNDS  175 

dish.  This  substance  has  much  of  the  appearance  and  some- 
thing of  the  taste  of  common  salt.  It  is  the  substance  known 
by  the  common  name  of  sal  ammoniac.  Chemical  analysis 
shows  that  its  composition  may  be  represented  by  the  for- 
mula NH4C1,  and  the  reaction  that  takes  place  may  be  ex- 
pressed in  the  following  equation  : 

NH4OH  +  HC1  ->-  NH4C1  +  H2O. 

This  reaction  is  much  like  the  one  between  sodium  hy- 
droxide and  hydrochloric  acid : 

NaOH  +  HC1  ->-  NaCl  +  H2O. 

Indeed,  ammonia  water  can  be  used  to  neutralize  any  of 
the  acids,  and  in  each  case  a  compound  which  closely  re- 
sembles the  corresponding  compound  formed  from  sodium 
hydroxide  and  the  same  acid  is  formed.  The  following 
compounds  may  be  taken  as  examples : 


SODIUM 
HYDROXIDE 

AMMONIUM 
HYDROXIDE 

Forms  with  sulphuric  acid 

Na2SO4 

(NH4)2SO4 

Forms  with  nitric  acid     

NaNO3 

NH4NO3 

Forms  with  carbonic  acid      .     .     . 

NasCOa 

(NH4)2C03 

These  compounds  are  known  as  ammonium  salts.  It 
will  be  noted  that  where  the  symbol  Na  appears  in  the 
formulas  of  the  sodium  salts,  the  group  NH4  is  found  in  the 
ammonium  salts.  A  group  like  this,  which  acts  as  a  unit 
in  chemical  reactions,  is  sometimes  called  a  radical.  The 
name  ammonium  has  been  given  to  the  radical  NH4,  and 
it  is  this  radical  which  takes  the  place  of  the  hydrogen  of 
the  acid  when  the  salt  is  formed.  In  reality  ammonium  is 
an  imaginary  substance,  for  no  one  has  succeeded  in  obtain- 


176  INORGANIC  CHEMISTRY 

ing  it  by  itself.  There  is  good  reason  to  believe,  however, 
that  it  exists  in  ammonium  salts  and  in  ammonia  water. 
All  ammonium  salts  are  decomposed  when  treated  with 
the  fixed  alkalies,  and  ammonia  is  given  off.  When 
ammonium  chloride  (sal  ammoniac)  is  heated  with  cal- 
cium hydroxide,  the  following  reaction  takes  place : 

Ca(OH)2  +  2  NH4C1  -»-  CaCl2  +  2  NH3  +  2  H2O. 

This  reaction  is  quite  commonly  used  in  the  preparation  of 
ammonia  for  study  in  the  laboratory. 

161.  Ammonium   chloride  or  sal  ammoniac   (NH4C1)   is 
prepared  by  passing  ammonia  gas  from  the  "  ammoniacal 
liquors"  (158)  into  a  solution  of  hydrochloric  acid.     It  is  a 
white,  granular,  or  crystalline  solid  with  a  sharp,  salty  taste. 
The  crude  salt  is  sometimes  called  muriate  of  ammonia.     It 
is  used  in  certain  kinds  of  electric  batteries,  in  medicine,  in 
soldering  fluids,  and  in  the  textile  industries.     When  heated, 
ammonium  chloride  is  converted  into  a  vapor  without  melt- 
ing, and  when  the  vapor  comes  in  contact  with  a  cold  sur- 
face, it  condenses  in  the  form  of  minute  crystals.     This 
process  of  vaporizing  and  condensing  a  solid  is  called  sub- 
limation, and  the  solid  is  said  to  sublimate.     All  ammonium 
salts  are  either  volatile  or  decompose  when  heated. 

162.  Ammonium  nitrate  (NH4NO3),  made  by  passing  am- 
monia into  a  solution  of  nitric  acid,  is  a  white  crystalline  solid, 
chiefly  used  in  the  preparation  of  nitrous  oxide  (152). 

163.  Ammonium  sulphate  ((NH4)2SO4)  is  made  by  passing 
the  ammonia  of  gas  works  into  a  solution  of  sulphuric  acid. 

2  NH4OH  +  H2S04  -»-  (NH4)2SO4  +  2  H20. 

It  is  a  grayish  yellow  salt  as  produced  commercially, 
and  is  the  most  widely  used  of  all  the  ammonium  salts.     It 


AMMONIA  AND  ITS  COMPOUNDS  177 

is  the  starting  point  in  the  production  of  many  of  the  am- 
monium compounds,  and  because  of  the  fact  that  it  is  rich 
in  nitrogen  it  is  also  largely  used  as  a  fertilizer. 

164.  Ammonium  carbonate  as  found  in  commerce  is  an 
impure  salt,  being  a  mixture  of  acid  ammonium  carbonate 
(NE^HCOs)  and  a  related  compound.     When  fresh  it  is  a 
transparent  solid;  but  on  exposure  to  the  air  it  gives  off 
ammonia  and  turns  white.     Smelling  salts  consist  of  lumps 
of  ammonium  carbonate  covered  with  alcohol   containing 
a  little  oil  of  lavender  or  other  perfume.      The  commercial 
carbonate    is   sometimes   used   instead   of  baking   powder. 
When  it  is  heated  the  acid  carbonate  dissociates,  forming 
water  and  the  two  gases  —  ammonia  and  carbon  dioxide : 

NH4HC03  ->•  H2O  +  NH3  +  C02. 

It  has  an  advantage  over  the  baking  powders  in  that  it 
leaves  no  solid  residue ;  but  considerable  experience  is  nec- 
essary to  handle  it.  successfully.  It  is  used  also  in  medi- 
cine and  in  scouring  wool,  and,  in  the  household,  for  soften- 
ing water.  It  is  sometimes  called  crystal  ammonia  or  solid 
ammonia,  although  the  substance  sold  under  the  name  of 
solid  household  ammonia  is  too  often  nothing  but  soda  with 
a  little  ammonium  carbonate  added  to  give  it  the  odor  of 
ammonia.  If  no  residue  remains  when  a  piece  of  the  ma- 
terial is  heated  it  is  pure  ammonium  carbonate. 

165.  Ice  Making  with  Ammonia.     All  liquids  absorb  heat 
when  they  evaporate   (8).     Ammonia  absorbs  very  large 
quantities  of  heat  in  changing  from  the  liquid  to  the  gaseous 
form,  and  this  fact  is  utilized  in  the  manufacture  of  artificial 
ice  (Fig.  107) .    Liquid  ammonia  is  forced  into  a  series  of  pipes 
(A)  which  are  submerged  in  a  large  tank  containing  brine. 
The  ammonia  vaporizes  and  in  so  doing  absorbs  the  required 

EV.  CHEM.  — 12 


178 


INORGANIC  CHEMISTRY 


heat  from  the  brine,  which  is  thus  cooled  below  the  freezing 
point  of  pure  water.  If  tin  cans  containing  water  are  hung 
in  this  brine,  the  water  will  be  frozen.  As  fast  as  the  am- 
monia gas  is  formed  in  the  cooling  pipes  it  is  removed  by  an 
exhaust  pump  and  is  liquefied  by  pressure  and  used  over  and 
over  again.  If  there  were  no  loss  by  leakage,  the  same 


FIG.  107.  —  The  manufacture  of  artificial  ice  by  the  ammonia  process. 

amount  of  ammonia  could  be  used  indefinitely.  When  the 
ammonia  condenses,  it  gives  off  heat,  which  is  removed 
by  running  cold  water  over  the  condensing  pipes  (B).  In 
cold  storage  warehouses  (Fig.  108)  the  cold  brine  is  made  to 
circulate  in  iron  pipes  through  the  rooms  to  be  cooled;  or 
the  pipes  in  which  the  ammonia  is  vaporized  may  be  placed 
in  these  rooms  instead  of  in  the  brine  tank. 

166.  Occurrence  of  Ammonia.  Although  there  are  so 
many  interesting  and  important  uses  for  ammonia  and  its 
compounds,  these  substances  are  found  only  in  very  small 
quantities  in  nature.  Ammonia  is  always  found  in  minute 


AMMONIA  AND   ITS  COMPOUNDS 


179 


traces  in  the  atmosphere,  because  it  is  one  of  the  products  of 
the  decay  of  plants  and  animals.  It  is  dissolved  in  rain 
water  and  carried  in- 
to the  soil,  where  it 
is  changed  first  into 
ammonium  com- 
pounds and  finally 
into  nitric  acid.  It 
is  found  also  in  mere 
traces  in  most  of  the 
natural  waters.  Its 
presence  in  water  in 
larger  quantities  is 
an  indication  that 
the  water  is  contam- 
inated by  sewage. 
Owing  to  the  insta- 
bility of  ammonium  compounds  and  the  ease  with  which 
they  are  changed  to  nitrates,  there  are  no  large  deposits  of 
ammonium  salts  as  there  are  of  nitrate  of  soda  (142). 

167.  Test  for  Ammonium  Salts.     These  salts  are  readily 
detected,  since  ammonia  is  evolved  when  they  are  treated 
with  a  dilute  solution  of  caustic  alkali,   such  as   sodium 
hydroxide.     The  ammonia  may  be  recognized  by  its  odor 
or  by  the  fact  that  it  turns  moist  red  litmus  paper  blue. 

168.  The  Nitrogen  Cycle.     Although  the  worker  in  the 
laboratory  has  difficulty  in  making  nitrogen  unite  with  other 
elements,  nature  evidently  has  methods  of  bringing  about 
this  union.     Small  quantities  of  nitric  acid  are  formed  dur- 
ing electric  storms,  and  this  is  carried  into  the  soil  by  means 
of  the  rains.     The  combined  nitrogen  added  to  the  soil  in 
this  way  amounts  to  only  three  to  eight  pounds  a  year  for 


FIG.  108.  —  Room  in  a  cold  storage  warehouse. 


180 


INORGANIC  CHEMISTRY 


each  acre  of  ground.  The  principal  factors  in  causing 
the  formation  of  nitrogen  compounds  are  the  bacteria 
that  live  in  the  soil.  An  ounce  of  a  good  garden  soil  is  said 
to  contain  at  least  one  hundred  fifty  millions  of  bacteria. 
These  are  very  small  one-celled  plants  that  can  be 


FIG.  109.  —  The  nitrogen  cycle  in  nature. 

seen  only  with  the  strongest  microscope.  Some  of  these 
bacteria  have  the  power  of  bringing  about  the  union  of  nitro- 
gen, oxygen,  and  water  to  form  nitric  acid,  which  acid 
(as  well  as  that  in  the  rain  water)  usually  unites  with  the 
calcium  carbonate  in  the  soil  to  form  calcium  nitrate,  thus : 

2  HNO3  +  CaCO3  ->-  Ca(NO3)2  +  H2O  +  CO2. 
All  plants  need  nitrogen  in  order  to  grow,  and  most  of 


AMMONIA  AND  ITS  COMPOUNDS  181 

them  obtain  their  nitrogen  from  the  soil  in  the  form  of  ni- 
trates. The  nitrogen  compounds  formed  by  these  bacteria, 
therefore,  are  used  by  the  higher  plants.  Some  plants, 
however,  have  another  way  of  obtaining  the  nitrogen  they 
need.  They  belong  to  the  family  of  plants  known  as  legumes, 
which  includes  the  clovers,  alfalfa,  peas,  and  beans.  On 
the  roots  of  these  plants  are  found  numbers  of  nodules  or 
tubercles,  which  consist  largely  of  masses  of  bacteria.  These 
bacteria,  while  living  on  the  roots  of  the  legumes,  have  the 
power  of  causing  the  nitrogen  of  the  air  to  form  a  chemical 
combination  which  the  plant  can  utilize.  Clovers  and  other 
legumes  are  frequently  grown  by  farmers  as  a  means  of 
increasing  the  nitrogen  compounds  in  the  soil.  This  power 
of  causing  free  nitrogen  to  enter  into  chemical  combination 
is  called  fixation  of  nitrogen.  Since  animals  get  all  the 
nitrogen  in  their  bodies  from  the  foods  consumed,  it  follows 
that  the  bacteria  are  either  directly  or  indirectly  responsible 
for  nearly  all  the  nitrogen  compounds  found  in  nature. 

Bacteria  are  responsible  also  for  other  changes  in  nitrogen 
compounds.  When  the  plants  or  animals  die,  their  bodies 
decay,  as  do  also  the  waste  products  of  the  animal  body. 
The  decay  is  caused  by  other  kinds  of  bacteria  and  results 
in  the  breaking  down  of  the  complex  nitrogen  compounds 
found  in  plants  and  animals.  Sometimes  the  nitrogen  is 
liberated  in  the  form  of  pure  nitrogen  or  of  ammonia  and 
finds  its  way  into  the  atmosphere.  This  change  is  called 
denitrification.  If  the  decay  takes  place  in  the  soil  it  is 
more  likely  to  result  .in  the  formation  of  nitrates,  which 
can  again  be  utilized  by  growing  plants.  This  change  from 
complex  nitrogen  compounds  to  nitric  acid  and  nitrates  is 
termed  nitrification.  The  change  is  caused  by  at  least 
three  kinds  of  bacteria  and  takes  place  in  three  steps: 


182  .  INORGANIC  CHEMISTRY 

(1)  the  formation  of  ammonium  compounds  from  the  or- 
ganic nitrogen  compounds;  (2)  the  change  of  ammonium 
compounds  into  nitrous  acid  (HNO2),  which  unites  with  a 
base  in  the  soil  to  form  a  nitrite — probably  calcium  nitrite, 
Ca(NOfe)2;  (3)  the  oxidation  of  the  nitrite  to  a  nitrate, 

Ca(N02)2  +  20^  Ca(N03)2. 

It  will  thus  be  observed  that  nitrogen  passes  through  a 
cycle  (Fig.  109)  much  like  that  described  for  carbon, 
although  the  amount  of  nitrogen  involved  in  these  changes 
is  much  smaller  than  the  carbon  of  the  carbon  cycle. 

169.  Another  Method  of  Fixing  Nitrogen.  When  cal- 
cium carbide  (CaC2)  is  strongly  heated  in  a  current  of  nitro- 
gen, a  substance  is  formed  which  has  the  formula  CaCN2 : 

CaC2  +  N2  ->-  CaCN2  +  C. 

This  new  substance  is  variously  named,  nitro-lime,  lime 
nitrogen,  and  calcium  cyanamide.  It  is  made  on  a  commercial 
scale  by  means  of  the  electric  furnace.  It  is  a  hard,  gray- 
black  mass  resembling  coke  and,  as  the  formula  shows,  is 
rich  in  nitrogen.  It  is  used  as  a  fertilizer,  but  before  the 
nitrogen  can  be  utilized  by  plants  it  must  be  oxidized  to 
nitrate,  a  process  which  readily  takes  place  in  the  soil  (624). 

EXERCISES 

Ex.  103.  Perform  the  experiment  described  in  paragraph  154. 
Why  is  the  gas  collected  by  upward  displacement  ?  How  does  the  gas 
affect  the  eyes  and  nose  ?  Test  the  gas  with  a  piece  of  red  litmus  paper. 
Will  the  gas  burn  or  support  combustion  ?  Does  it  dissolve  in  water  ? 
Can  it  be  condensed  to  a  liquid  ?  What  is  its  name  and  formula  ? 

Ex.  104.  Heat  bits  of  meat,  hair,  horn,  and  some  beans  in  hard 
glass  test  tubes.  Test  the  vapor  from  the  tubes  with  moist  red  litmus 
paper.  What  is  the  source  of  the  ammonia  ?  Was  the  nitrogen  present 
in  the  above  materials  as  ammonia  ?  Is  ammonia  formed  by  the  decay 


AMMONIA  AND   ITS  COMPOUNDS  183 

of  animal  and  vegetable  matter?  What  is  the  composition  by  weight 
of  ammonia  ?  How  is  the  ammonia  water  of  commerce  manufactured  ? 
Ex.  105.  Examine  a  sample  of  ammonia  water  from  home.  How 
does  it  feel  when  rubbed  between  the  fingers  ?  What  is  the  odor  ? 
The  reaction  with  litmus  paper  ?  Is  it  an  alkali  ?  Why  is  it  called  a 
volatile  alkali?  Is  its  volatility  any  advantage  in  cleaning?  Does 
ammonia  gas  merely  dissolve  in  water  or  form  a  chemical  compound 
with  it  ?  Write  the  reaction.  Is  this  compound  stable  ?  Why  does 
ammonia  water  always  give  the  odor  of  ammonia  gas?  How  much 
ammonia  does  the  ordinary  household  ammonia  water  contain  ? 

Ex.  106.  To  a  dilute  solution  of  hydrochloric  acid,  add  dilute 
ammonia  water  until  the  mixture  is  neutral  or  faintly  alkaline.  Evap- 
orate to  dryness.  What  remains?  Give  the  formula.  Write  re- 
action between  ammonium  hydroxide  and  hydrochloric  acid.  Will 
ammonia  water  form  salts  with  other  acids?  Compare  with  sodium 
salts  of  the  same  acids.  What  is  a  radical?  What  is  the  name  of 
the  radical  NH4  ?  Does  this  radical  exist  ?  Mix  a  little  ammonium 
chloride  with  lime  and  heat  in  a  test  tube.  Try  the  same  experiment 
with  ammonium  sulphate  and  sodium  hydroxide.  How  do  ammonium 
salts  act  when  heated  with  the  fixed  alkalies  ? 

Ex.  107.  Place  a  teaspoonful  of  ammonium  chloride  in  a  long  test 
tube.  Hold  the  test  tube  in  an  inclined  position  and  heat.  What 
happens  to  the,  chloride  ?  Does  it  condense  again  at  the  top  of  the 
test  tube?  What  is  meant  by  sublimation?  What  are  the  commer- 
cial uses  of  ammonium  chloride? 

Ex.  108.  Examine  some  ammonium  sulphate.  How  is  it  made 
commercially?  What  are  its  uses?  Does  ammonia  combine  with 
carbonic  acid?  Examine  crystals  of  crude  ammonium  carbonate. 
Why  is  it  called  sal  volatile?  What  happens  to  it  when  heated? 
Write  the  reaction.  What  uses  are  made  of  it?  f  Examine  a  commer- 
cial sample  of  "  solid  household  ammonia  "  and  determine  whether 
it  contains  soda.  How  should  you  test  for  ammonium  salts  ? 

Ex.  109.  Explain  by  help  of  a  diagram  how  liquid  ammonia  is 
utilized  in  ice  making. 

Ex.  110.  Where  and  to  what  extent  is  ammonia  found  in  nature  ? 
Why  is  it  not  more  abundant  ?  Discuss  the  cycle  of  nitrogen  in  nature. 
What  is  formed  when  calcium  carbide  is  strongly  heated  in  a  current  of 
n:trogen  ?  What  use  is  made  of  calcium  cyanamide  ? 


CHAPTER  XVIII 


PHOSPHORUS,  PHOSPHORIC  ACID,  ARSENIC 

170.  PHOSPHORUS  has  already  been  used  in  the  experi- 
ments with  oxygen  (37).  It  is  an  element  that  is  never  found 
in  the  free  state,  and  is  usually  combined  with  calcium  and 
oxygen  in  the  form  of  calcium  phosphate. 

Phosphorus  is  slightly  yellow  and  translucent.  It  can  be 
cut  like  wax  at  ordinary  temperatures,  and  it  melts  at  44°  C. 
It  is  insoluble  in  water  but  dissolves  freely  in  carbon  bisul- 
phide. It  is  very  poisonous;  and  in  fac- 
tories where  phosphorus  is  made,  the  work- 
men are  frequently  poisoned  by  it. 

In  contact  with  the  air  phosphorus  gives 
off  fumes  which  emit  light  visible  in  a  dark 
room.  This  phenomenon  suggested  the  name 
phosphorus,  which  is  derived  from  the  Greek 
and  means  "  light  bearer."  Although  other 
substances  act  in  the  same  way,  this 
property  was  first  observed  in  connection 
FIG.  no.— sticks  of  with  phosphorus  and  the  phenomenon  is, 

therefore,  called  phosphor 'esence. 

The  streak  of  light  left  by  a  match  when  rubbed  on  any 
surface  in  a  dark  room  is  due  to  the  phosphorus  in  the  match. 
Phosphorus  takes  fire  when  rubbed  or  cut ;  hence  it  must 
be  handled  with  great  care.  It  is  kept  under  water,  and 
should  be  cut  under  water  and  never  held  in  the  hand,  since 
the  heat  of  the  hand  is  sufficient  to  ignite  it.  The  burns 

184 


PHOSPHORUS  185 

caused  by  phosphorus  are  very  difficult  to  heal.  In  a  finely 
divided  state  phosphorus  ignites  spontaneously.  If  a  little 
phosphorus  is  dissolved  in  carbon  bisulphide  and  the  solu- 
tion poured  on  a  piece  of  filter  paper,  the  phosphorus  will 
take  fire  as  soon  as  the  carbon  bisulphide  has  evaporated. 

171.  Red   Phosphorus.     When   ordinary   phosphorus   is 
exposed  to  the  light  for  a  long  time,  it  becomes  opaque  and 
darker  in  color,  and  finally  dark  red.     The  change  to  red 
phosphorus  can  be  hastened  if  the  yellow  variety  is  heated 
in  a  sealed  tube  to  about  250°  C.     Red  phosphorus  is  strik- 
ingly different  in  its  behavior  from  the  yellow.     It  is  not 
very  active.     It  does  not  change  in  the  air,  and  must  be 
heated  to  a  comparatively  high  temperature  before  it  will 
combine  with  oxygen.      It  is  insoluble  in  carbon  bisulphide 
and  is  not  poisonous.     Red  phosphorus  may  be  changed  back 
to  the  ordinary  variety  by  heating  it  to  300°  C.  in  an  atmos- 
phere of  nitrogen. 

172.  Preparation  of  Phosphorus.     The  ash  produced  by 
burning  bones  is  the  source  of  most  of  the  phosphorus  of 
commerce.     Phosphorus  cannot  be  readily  prepared  in  the 
laboratory.     Commercially  it  is  made  by  heating  bone  ash 
with   sand   and   charcoal.     A   complicated   reaction   takes 
place  during  which  phosphorus  is  liberated  as  the  element  and 
escapes  from  the  retort  as  a  vapor  which  is  condensed  under 
water.     It  is  purified  by  redistillation  and  cast  into  sticks 
under  water.     These  sticks  are  usually  about  half  an  inch 
in  diameter  and  7.5  inches  long. 

173.  Matches.     The  principal  use  of  phosphorus  is  in 
the  manufacture  of  matches.     The  ordinary  parlor  matches 
are  made  by  dipping  small  pieces  of  wood  into  melted  par- 
affin and  then  into  a  mixture  of  phosphorus,  manganese 
dioxide,  and  glue.     By  rubbing  such  matches  on  a  rough 


186  INORGANIC   CHEMISTRY 

surface  enough  heat  is  generated  by  the  friction  to  cause 
the  phosphorus  to  ignite.  This  sets  fire  to  the  paraffin, 
which  in  turn  kindles  the  wood.  The  manufacture  of  these 
matches  is  prohibited  in  some  countries  because  they  are  so 
liable  to  take  fire  and  because  the  workmen  in  the  factories 
are  so  often  poisoned  by  the  phosphorus.  Safety  matches, 
or  Swedish  matches,  contain  no  yellow  phosphorus.  The 
head  of  this  kind  is  a  mixture  of  potassium  chlorate,  anti- 
mony sulphide,  and  glue.  The  side  of  the  box  is  coated  with 
red  phosphorus,  glue,  and  powdered  glass.  When  the  head 
of  the  match  is  drawn  over  this  prepared  surface,  a  little  of 
the  phosphorus  is  torn  off,  catches  fire,  and  ignites  the  match. 
Safety  matches  cannot  easily  be  ignited  except  on  the  pre- 
pared surface,  although  they  can  be  lighted  by  drawing 
them  rapidly  over  glass. 

174.  Phosphorus  burns  with  the  formation  of  a  dense 
white  cloud,  which  condenses  into  a  white,  snowlike  solid. 
Either  variety  of  phosphorus  burns  readily,  but  the  com- 
bustion of  the  yellow  is  much  more  violent.     The  product  of 
combustion,  which  is  the  same  in  either  case,  has  the  com- 
position P2O5  and  is   called  phosphorus  pentoxide.     This 
oxide  of  phosphorus  is  very  deliquescent,  quickly  drawing 
moisture  from  the  air.     It  combines  vigorously  with  water, 
with  a  hissing  sound.     It  is  often  used  in  the  laboratory  to 
dry  gases. 

175.  Phosphoric  Acid.     When  phosphorus  pentoxide  is 
added  to  hot  water,  the  solution  has  a  sour  taste  and  turns 
blue  litmus  paper  red.     This  is  due  to  the  fact  that  the  phos- 
phorus pentoxide  has  combined  with  the  water  to  form  phos- 
phoric acid,  H3PO4 : 

P2O5  +  3  H2O  ->-  2  H3PO4. 


PHOSPHORUS  AND  PHOSPHORIC  ACID  187 

Phosphoric  acid,  also  called  orthophosphoric  acid,  when 
pure  is  a  white  solid  that  is  very  soluble  in  water.  The 
commercial  article  contains  a  little  water  and  is  a  thick, 
sirupy  liquid  somewhat  resembling  pure  sulphuric  acid  in 
appearance  and  weight.  While  it  can  be  prepared  as  in- 
dicated above,  it  is  usually  made  by  the  common  method  for 
preparing  acids ;  namely,  by  the  action  of  sulphuric  acid  on 
one  of  the  salts  of  phosphoric  acid.  The  salt  ordinarily 
used  is  calcium  phosphate,  Ca3(PO4)2,  which  is  a  constituent 
of  bones  and  of  the  phosphate  rocks. 

Ca3(PO4)2  +  3  H2SO4  ->-  3  CaSO4  +  2  H3PO4. 

The  calcium  sulphate  is  insoluble  and  is  filtered  off. 

176.  Salts  of  Phosphoric  Acid.  The  formula  for  phos- 
phoric acid,  H3PO4,  shows  that  each  molecule  contains  three 
hydrogen  atoms.  From  what  was  said  about  normal  and 
acid  salts  (140)  it  is  evident  that  one,  two,  or  three  of  these 
hydrogen  atoms  might  be  replaced  by  a  metal.  There  are, 
therefore,  three  possible  phosphates  of  each  metal.  The 
three  phosphates  of  sodium,  for  example,  with  their  formulas 
and  chemical  names  are  as  follows : 

Mono-sodium  phosphate,  NaH2PO ; 

Di-sodium  phosphate,  Na2HPO4 ; 

Normal  or  Tri-sodium  phosphate,  Na3PO4. 

The  second  salt,  di-sodium  phosphate,  is  the  most  common, 
and  is  the  one  used  in  the  laboratory  and  in  medicine.  It 
is  usually  known  simply  as  sodium  phosphate.  It  crystal- 
lizes with  twelve  molecules  of  water  of  crystallization : 

Na^HPO,  - 12  H2O. 

In  the  case  of  a  metal  like  calcium,  which  has  a  valence  of 
two,  the  manner  in  which  the  base  and  acid  combine  to  form 


188 


INORGANIC  CHEMISTRY 


the  salts  is  not  so  apparent.  For  the  bivalent  calcium  just 
to  neutralize  phosphoric  acid  with  its  three  hydrogen  atoms, 
it  must  be  assumed  that  three  atoms  of  calcium  react  with 
two  molecules  of  phosphoric  acid,  thus  : 

3  Ca  +  2  H3PO4  ->-  Ca3(PO4)2  +  6  H. 
The  three  calcium  salts  and  their  formulas  are, 

Monocalcium  phosphate,  CaH4(PO4)2, 
Dicalcium  phosphate,  Ca2H2(PO4)2, 
Normal  or  Tricalcium  phosphate,  Ca3(PO4)2. 

177.  Occurrence  of  Phosphorus.    The  bulk  of  all  the 
phosphorus  found  in  nature  exists  in  the  form  of  tricalcium 

phosphate.  The  bones 
of  animals  are  80  per 
cent  tricalcium  phos- 
phate. It  occurs  in 
large  deposits  in  a 
mineral  known  as  apa- 
tite, and  in  a  more 
impure  form  it  is 
found  in  the  phosphate 
rocks  of  Florida,  Ten- 
nessee, South  Caro- 
lina, Arkansas,  Ken- 
tucky, Idaho,  Utah, 
Wyoming,  and  Montana.  The  rocks  from  which  the 
soils  were  formed  contained  some  tricalcium  phosphate 
also,  and  consequently  it  is  present  in  small  quantities  in 
all  soils. 

Phosphorus  is  found  in  plant  and  animal  tissue.     The 
plants  derive  it  from  the  phosphate  in  the  soil  and  build 


FIG.  111.  — Hydraulic  mining  of  phosphate  rock 
in  Florida. 


PHOSPHORUS  189' 

it  up  into  complex  organic  compounds.  Animals  eat  the 
plants  and  get  their  phosphorus  in  that  way.  When  plant 
residues  and  the  animal  bodies  and  manures  decay,  the 
phosphorus  is  returned  to  the  soil,  where  it  is  again  oxidized 
to  phosphates ;  thus  it  completes  the  phosphorus  cycle. 

Some  of  the  iron  ores  contain  phosphorus,  which  is  ob- 
jectionable in  the  manufacture  of  steel.  To  remove  it 
lime  is  added,  and  the  phosphorus  remains  with  the  calcium 
in  the  slag,  which  is  ground  to  a  fine  powder  and  sold  as 
basic  slag,  Thomas  phosphate,  or  odorless  phosphate  (236). 

178.  Fertilizers.  Phosphorus  in  the  form  of  a  phosphate 
is  absolutely  essential  to  plant  growth.  Very  few  soils 
contain  sufficient  phosphorus  for  a  maximum  crop,  and  as  a 
large  part  of  the  phosphorus  in  the  plant  is  stored  in  the 
seeds,  which  are  removed  from  the  land,  the  amount  of 
phosphorus  in  the  soil  is  being  constantly  decreased.  A 
part  of  the  phosphorus  is  returned  to  the  soil  in  animal 
manures,  but  never  a  sufficient  amount  to  restore  that  re- 
moved by  the  crops.  To  maintain  a  satisfactory  crop 
yield,  the  farmer  must  add  some  form  of  calcium  phosphate 
to  the  soil.  This  is  sometimes  done  by  the  use  of  bones, 
which  are  ground  to  a  fine  powder  (bone  meal),  or  by  the 
use  of  basic  slag.  The  phosphate  rocks  are  also  ground 
to  a  fine  powder  called  floats  and  applied  directly  to  the 
land  or  mixed  with  the  animal  manures.  Tricalcium  phos- 
phate, however,  is  very  insoluble  in  water,  and  to  make 
it  more  available  it  is  customary  to  treat  it  with  sufficient 
sulphuric  acid  to  bring  about  the  following  reaction: 

Ca3(PO4)2  +  2  H2SO4  -*-  2  CaSO4  +  CaH4(PO4)2. 

Monocalcium  phosphate,  CaH4(PO4)2,  is  soluble  in  water 
and  can,  therefore,  be  much  better  distributed  in  the  soil 


190  INORGANIC  CHEMISTRY 

than  the  insoluble  natural  phosphate.  The  calcium  sul- 
phate (gypsum)  and  monocalcium  phosphate  produced  by 
the  above  reaction  are  not  separated,  but  the  mixture  is 
dried  and  ground,  and  sold  under  the  various  names  of 
superphosphate,  acid  phosphate,  or  acidulated  rock  (610). 

179.  The  term   phosphoric    acid    as    used    in    fertilizers 
does  not  mean  H3PO4  but  the  anhydride  P2O5  (141).     For- 
merly calcium  phosphate  was  considered  to  be  a  combina- 
tion of  lime  and  phosphoric  anhydride.     The  formula  was 
written  3  CaO  •  P<£)S.     The  name  phosphoric  acid  was  then 
given  to  the  oxide  P2O5,  and  although  this  use  of  the  name 
has  been  discontinued  by  chemists,  it  has  persisted  in  trade. 
When  a  fertilizer,  then,  is  said  to  contain  14  per  cent  of 
phosphoric  acid,  it  means  that  it  contains  calcium  phosphate 
equivalent  to  14  per  cent  of  P2C>5. 

180.  Test  for  Phosphoric   Acid   or  Phosphate.     If  the 
phosphate  is  insoluble  in  water,  it  should  be  dissolved  in 
dilute  nitric  acid.     To  the  solution  to  be  tested  nitric  acid 
should  be  added  unless  it  was  used  to  dissolve  the  substance. 
Add  about  2  cc.  of  the  ammonium  molybdate  test  solution 
and  warm  gently.     If  phosphoric  acid  is  present,  a  yellow 
precipitate  will  be  formed.     Since  the  composition  of  the  pre- 
cipitate depends  upon  the  temperature,  however,  no  formula 
can  be  assigned  to  it. 

181.  Arsenic.     The  name   arsenic,   which  is   sometimes 
used  for  the  white  material  sold  in  the  drug  stores,  should 
be  confined  to  the  element  arsenic,  which  is  a  steel  gray, 
brittle    solid,    with    a    metallic    appearance.     It    is    found 
sparingly  in  the  uncombined  state,  but  its  compounds  with 
sulphur  and  with  the  metals  are  very  abundant.     It  is  not 
in  common  use,  but  it  is  sometimes  added  to  lead  as   a 
hardener  in  the  manufacture  of  shot. 


ARSENIC  191 

182,  White  Arsenic.     When  arsenic,  or  any  of  its  ores, 
is  burned,  the  arsenic  is  converted  into  the  oxide : 

2  As  +  3  O  -*-  AssOs. 

Arsenic  trioxide  (As2O3)  is  the  substance  ordinarily  called 
arsenic,  or  white  arsenic.  It  is  found  in  trade  as  a  white 
powder  which  has  no  odor  and  a  faintly  sweet  taste.  It 
is  a  deadly  poison  and  should  be  handled  with  great  care. 
It  is  slightly  soluble  in  water  and  the  solution  is  poisonous 
to  both  plants  and  animals.  Arsenic  compounds  are  used  al- 
most entirely  for  the  destruction  of  vermin  and  insect  pests. 

183.  Arsenites.     When  arsenic  trioxide  is  boiled  with  so- 
dium hydroxide,  the  following  reaction  takes  place  : 

AsaOs  +  6  NaOH  ->-  2  Na3As03  +  3  H2O. 
Sodium  arsenite,  NaaAsOs,  is  soluble  in  water  and  is  used  as 
a  basis  for  the  preparation  of  other  compounds  of  arsenic. 
As  it  is  very  soluble  it  is  more  intensely  poisonous  than 
white  arsenic.  The  corresponding  calcium  salt,  calcium 
arsenite,  Ca3(AsO3)2,  is  insoluble  and  is  often  used  as  a  spray 
to  kill  potato  bugs  and  other  insects.  It  is  made  by  adding  a 
solution  of  sodium  arsenite  to  calcium  hydroxide  (slaked  lime) . 
Sodium  arsenite  upon  oxidation  is  changed  to  the  arse- 
nate,  Na3AsO4.  Evidently  this  compound  is  the  sodium 
salt  of  arsenic  acid,  H3AsO4,  while  sodium  arsenite  is  the 
salt  of  arsenious  acid,  H3AsO3.  Neither  pf  these  acids  is 
of  any  importance ;  but  several  of  their  salts  are  in  common 
use.  The  arsenites  and  arsenates  of  all  metals  except  sodium 
and  potassium  are  insoluble.  Some  of  them  will  be  studied 
in  connection  with  the  metals  from  which  they  are  formed. 

EXERCISES 

Ex.  111.     What  is  the  appearance  of  ordinary  phosphorus?     Is  it 
ever  found  in  nature  in  the  elemental  condition?     Is  it  soluble  in 


192 


INORGANIC  CHEMISTRY 


water?  What  effect  does  it  have  upon  the  men  who  work  with  it? 
What  happens  to  phosphorus  when  exposed  to  the  ah*?  Why  was 
it  named  phosphorus?  Why  is  it  stored  under  water?  When  or- 
dinary phosphorus  is  heated  in  a  sealed  tube  what  change  takes  place  ? 
Is  the  red  phosphorus  very  active?  In  what  other  respects  does  it 
differ  from  ordinary  phosphorus?  How  is  phosphorus  prepared  com- 
mercially ?  How  are  the  safety  matches  made  ? 

(Note.  All  experiments  with  yellow  phosphorus  should  be  per- 
formed by  the  teacher.) 

Ex.  112.  Burn  a  little  red  phosphorus  in  a  dry  wide-mouth  bottle 
(Fig.  112).  What  is  formed?  What  is  the  composition  of  the  white 
fumes  ?  The  name  ?  Pour  a  little  water  into 
the  bottle  and  shake.  Does  the  white  material 
dissolve?  Test  solution  with  blue  litmus 
paper.  Write  equation  for  action  of  phos- 
phorus pentoxide  on  water.  Examine  the  phos- 
phoric acid  of  the  laboratory.  How  is  it  pre- 
pared commercially  ?  How  many  atoms  of  hy- 
drogen in  the  molecule?  How  many  sodium 
phosphates  are  possible  ?  Names  and  formulas  ? 
Ex.  113.  Dissolve  a  little  sodium  phos- 
phate in  water.  Heat  and  add  a  few  drops  of 
the  ammonium  molybdate  reagent  of  the  lab- 
oratory. What  happens  ?  This  is  the  test  for 
a  phosphate.  Mix  some  rock  phosphate  with 
water.  Filter  and  test  the  filtrate  for  phos- 
phates. Moisten  another  sample  of  the  rock 
phosphate  with  sulphuric  acid.  After  ten 
minutes  add  water,  stir,  and  filter.  Test  this  filtrate  for  phosphates. 
Have  you  any  evidence  that  the  sulphuric  acid  made  the  rock  phos- 
phate soluble  ?  Why  is  rock  phosphate  treated  with  sulphuric  acid 
in  making  fertilizers  ?  What  is  meant  by  acid  phosphate,  or  acidulated 
rock?  Discuss  the  occurrence  of  phosphorus  in  nature.  What  is 
meant  by  the  term  phosphoric  acid  as  used  in  the  fertilizer  trade  ? 

Ex.  114.  What  is  the  composition  of  the  substance  known  as  white 
arsenic?  What  is  its  chemical  name?  What  is  formed  when  it  is 
boiled  with  sodium  hydroxide?  What  is  formed  when  the  arsenites 
are  oxidized  ?  What  practical  use  is  made  of  calcium  arsenite  ? 


FIG.    112.  —  Burning 
phosphorus  in  bottle. 


CHAPTER  XIX 
SAND,   SILICON,  BORAX 

184.  Sand.  The  term  sand  is  sometimes  used  to  desig- 
nate any  gritty  material  consisting  of  small  angular  frag- 
ments of  rocks  or  minerals.  In  a  more  restricted  sense 
sand  consists  of  small  particles  of  more  or 
less  pure  silica.  In  its  pure  form  silica 
crystallizes  in  beautiful  six-sided  prisms 
and  is  called  quartz,  or,  sometimes,  rock 
crystal.  These  crystals  are  often  so  clear 
that  they  can  be  used  for  making  spectacle 
lenses  or  as  substitutes  for  the  diamond. 
Sea  sand  is  often  almost  exclusively  frag- 
ments of  quartz.  White  sands  are  prac- 
tically pure  silica,  while  in  the  yellow 
sands,  or  the  variously  tinted  sandstones, 
the  silica  is  colored  by  iron  oxide  or  some 
other  metallic  oxide. 

Chemically,  silica  is  an  oxide  of  the 
element  silicon  and  is  called  silicon  dioxide,, 
which  has  the  composition  represented  by 
the  formula  SiO2.  Quartz  is  the  most  common  of  minerals 
and  constitutes  18  per  cent  of  the  crust  of  the  earth.  In  the 
form  of  the  mineral,  quartzite,  it  forms  many  mountains, 
and  the  sandstones  also  consist  almost  entirely  of  silica. 
Several  of  the  valuable  stones  and  precious  gems,  as  onyx, 
or  carnelian,  agate,  jasper,  flint,  amethyst,  rhinestone,  and 
EV.  CHBM; — 13  193 


FIG.   113.  —  Quartz 
crystal. 


194  INORGANIC   CHEMISTRY 

opal,  consist  of  silicon  dioxide.  Infusorial  earth  consists  of 
the  skeletons  of  minute  aquatic  organisms  and  is  nearly 
pure  silicon  dioxide.  It  is  employed  as  a  scouring  and 
polishing  material,  and  is  used  to  absorb  nitroglycerin  in 
the  manufacture  of  dynamite.  Silica  also  occurs  in  the 
leaves  and  stalks  of  grasses,  cereals,  and  bamboos  and  other 
canes.  The  plant  known  as  equisetum  (horsetail)  contains 
so  much  silica  that  it  is  often  used  for  scouring  and  is  called 
scouring  rush.  Silica  constitutes  about  40  per  cent  of  the 
ash  of  the  feathers  of  birds  and  is  found  in  the  hair  of  animals. 

185.  Silicon.     The  element  silicon  is  never  found  in  the 
free  state,  although,  next  to  oxygen,  it  is  the  most  abundant 
element.     The  solid  crust  of  the  earth  contains  28  per  cent 
of  silicon ;  for  it  is  found  in  all  varieties  of  granite,  sandstone, 
gneiss,   clay,  and  shale.     It  may  be  prepared  by  heating 
the  oxide  (quartz  or  white  sand)  with  powdered  magnesium. 

SiO2  +  2  Mg  ->-  Si  +  2  MgO. 

Silicon  made  in  this  way  is  an  amorphous  brown  powder 
insoluble  in  water  and  in  all  the  common  acids.  It  is  used 
to  some  extent  in  the  steel  industry  as  a  reducing  agent. 
When  heated  to  a  high  temperature,  it  burns  and  forms 
silicon  dioxide  (SiO2). 

186.  Water  Glass.    When  clean  white  sand  is  melted 
with  sodium  carbonate,  carbon  dioxide  escapes,  and  a  com- 
pound remains  which  is  called  sodium  silicate  (NaaSiOs). 

NagCOa  +  SiO2  •*-  Na*SiO3  +  CO2. 

Sodium  silicate  is  soluble  in  water  and  is  known  as  water 
glass.  In  commerce  it  is  found  as  a  thick,  sirupy  solution. 
It  is  employed  in  fireproofing  cloth  and  wood,  as  a  cement, 
as  a  "  filler  "  in  laundry  soaps  (462),  and  in  preserving  eggs. 
For  the  latter  purpose  the  commercial  solution  is  diluted  with 


SAND  AND  SILICON 


195 


nine  times  its  own  volume  of  water,  and  the  eggs  are  kept 
immersed  in  the  liquid  until  used.  If  the  eggs  are  perfectly 
fresh  at  the  beginning,  they  can  be  preserved  for  several 
months  in  this  solution. 

187.  Silicic  Acid.     If  sulphuric  or  hydrochloric  acid  is 
added  to  a  concentrated  solution  of  water  glass,  silicic  acid 
separates  in  the  form  of  a  jelly,  thus : 

Na2SiO3  +  H2SO4  ->-  Na2SO4  +  H2SiO3. 
Silicic  acid  has  never  been  prepared  in  a  pure  state  because 
when  evaporated  to  dryness  it  decomposes,  and  pure  white 
sand  (silicon  dioxide)  remains  in  the  dish : 

H2SiO3  -^H2O  +  SiO2. 

188.  Glass.     When  limestone  is  heated  at  a  high  tem- 
perature with  sand,  calcium  silicate  is  formed  and  carbon 
dioxide  is  given  off: 

CaCO3  +  SiO2  -»-  CaSiO3  +  CO2. 

If  both  calcium  and  sodium  carbonates  are  melted  with  sand, 
the  product  is  a  mixture  of  sodium  and  calcium  silicates 
which,  upon  cooling, 
forms  ordinary  win- 
dow glass.  The  in- 
gredients are  used 
in  about  the  fol- 
lowing proportions : 
clean  sand,  150 
pounds ;  soda,  50 
pounds ;  limestone, 
25  pounds.  Window 
glass  is  made  by 
blowing  a  lump  of  the  glass  into  a  hollow  cylinder,  which 
is  then  cut  lengthwise  and  allowed  to  spread  open  upon  a 


FIG.  114.  —Glass  blowing. 


196  INORGANIC   CHEMISTRY 

flat  surface.  Plate  glass  has  the  same  composition  but  is 
made  by  pouring  the  molten  glass  upon  a  large  table  and 
rolling  it  with  a  hot  iron  roller,  and  subsequently  grinding 
and  polishing  it. 

When  potash  is  used  in  place  of  the  soda,  a  very  hard 
glass  is  formed  known  as  Bohemian  glass,  which  is  much 
used  for  chemical  apparatus.  Lamp  chimneys,  lenses,  and 
cut  glass  are  made  of  flint  glass.  This  is  a  silicate  of  lead 
and  potassium,  made  by  melting  potassium  carbonate  and 
lead  oxide  with  sand.  Glass  is  colored  by  adding  different 
substances  which  dissolve  in  the  molten  mass.  The  green 
color  of  common  glass  bottles  is  due  to  the  iron  in  the  impure 
sand  used;  copper  and  cobalt  produce  different  shades  of 
blue;  manganese  dioxide  gives  a  pink  or  violet  color,  and 
certain  copper  compounds  and  gold  make  the  glass  ruby  red. 

189.  Natural  Silicates.  The  salts  of  silicic  acid  are  called 
silicates.  They  make  up  a  large  part  of  the  earth's  crust,  the 
silicates  of  aluminum,  calcium,  potassium,  sodium,  mag- 
nesium, and  iron  being  the  most  abundant.  Nearly  all 
the  common  rocks,  with  the  exception  of  limestone  and 
dolomite,  are  silicates,  as  well  as  many  of  the  minerals  and 
a  few  of  the  precious  gems.  Mica,  clay,  slate,  asbestos, 
soapstone,  feldspar,  meerschaum,  garnet,  emerald,  topaz, 
and  beryl  are  all  silicates.  Some  of  these  silicates  are  salts 
of  the  silicic  acid  (H2SiO3)  mentioned  above,  but  many  of 
them  are  evidently  salts  of  acids  which  are  very  much  more 
complex.  Silicates  are  known,  for  instance,  which  corre- 
spond to  acids  having  the  formulas  H^SiO^  HcSi2O7,  H4Si3O8, 
and  many  others.  None  of  these  more  complex  acids  have 
ever  been  isolated,  but  their  salts  are  well  known,  and  some 
of  them  will  be  described  when  the  metals  from  which  they 
are  formed  are  studied. 


SAND  AND   SILICON  197 

When  the  silicic  acid  contains  four  or  more  hydrogen 
atoms,  it  is  quite  common  to  find  that  two  or  more  metals 
have  replaced  the  hydrogen  atoms  to  form  a  mixed  salt. 
For  example,  feldspar  is  a  silicate  of  potassium  and  alumi- 
num (KAlSi3O8) ;  and  mica  is  another  silicate  of  potassium 
and  aluminum  (KAlSi04). 

190.  Decomposing  the  Silicate.     All  the  silicates,  with 
the  exception  of  those  of  sodium  and  potassium,  are  in- 
soluble in  water.     Most  of  them  are  also  quite  insoluble  or 
very  slightly  soluble  in  acids.     If  an  insoluble  silicate  is 
mixed  with  sodium  carbonate  and  the  mixture  is  heated, 
it  melts  or  fuses,  and  sodium  silicate  and  an  insoluble  car- 
bonate are  formed ;  that  is,  the  sodium  and  the  other  metals 
change  places. 

CaSiO3  +  N^COs  -»-  CaC03  +  Na^SiOs. 

The  sodium  silicate  can  be  dissolved  in  hot  water,  leaving 
the  metals  of  the  original  silicate  behind  as  carbonates, 
which  can  be  dissolved  in  hydrochloric  acid.  This  is  the 
method  used  in  the  laboratory  to  decompose  the  silicates 
for  purposes  of  analysis. 

191.  Test  for  Silica  or  Silicates.    If  the  material  is  in- 
soluble in  water  or  acids,  it  is  fused  with  sodium  carbonate 
and  then  treated  with  boiling  water  as  deacribed  in  the  pre- 
vious paragraph  (190).     Hydrochloric  acid  is  then  added 
to  the  hot  water  solution  with  the  result  that  the  gelatinous 
silicic  acid  separates;  or  the   acidulated  solution  may  be 
evaporated  to  dryness,  upon  which  a  white  residue  of  silica 
(SiO2)  remains  which  cannot  be  dissolved  in  water  and  hydro- 
chloric acid.     No  substance  but  silicic  acid  behaves  in  this 
way  when  treated  with  hydrochloric  acid. 


198  INORGANIC  CHEMISTRY 

192.  Carborundum.     When  quartz  sand  is  strongly  heated 
with  coke  in  an  electric  furnace,  the  silicon  and  carbon 
combine  to  form  a  compound  which  is  silicon  carbide  : 

SiO2  +  3  C  ->-  SiC  +  2  CO. 

Silicon  carbide,  SiC,  is  the  substance  known  under  the  trade 
name  of  carborundum.  It  is  used  as  a  substitute  for  emery 
in  hones  and  whetstones,  in  grinding  wheels,  and  in  polish- 
ing papers  and  powders.  It  is  much  harder  than  emery, 
being  almost  as  hard  as  the  diamond. 

193.  Borax.     The  familiar  substance  borax  is  found  in 
California  and  in  Tibet,  but  most  of  the  commercial  borax 
is  prepared  from  a  mineral  known  as  calcium  borate.     Borax 
is  sodium  borate,  a  compound  of  sodium,  oxygen,  and  the 
element  boron  (Na2B4O7-  10  H2O).     It  is  a  white  crystallized 
solid,  containing  ten  molecules  of  water  of  crystallization. 
It  effloresces  in  the  air.     It  is  employed  as  a  cleansing  ma- 
terial in  the  laundry  and  is  used  in  some  soaps.     It  is  also 
used  as  a  preservative  in  certain  canned  products,  but  such 
use  is  objectionable.     It  is  used  in  soldering  and  welding, 
since  it  dissolves  any  oxide  that  may  be  on  the  metal  and  thus 
keeps  the  surface  clean,  a  condition  that  is  absolutely  neces- 
sary in  order  that  the  solder  may  adhere. 

194.  Boric  Acid.     If  dilute  sulphuric  acid  is  added  to 
borax,  the  following  reaction  takes  place  : 

H2SO4  +  5  H2O  ->-  NaaSO4  +  4  H3BO3. 


Boric  acid,  HsBOs,  forms  white  scaly  crystals  that  feel  greasy 
to  the  touch.  It  dissolves  slightly  in  cold  water,  but  is 
readily  soluble  in  hot  water  and  in  alcohol.  Boric  acid 
is  sometimes  known  commercially  as  boracic  acid.  It  is  used 
as  an  antiseptic  in  medicine  and  surgery.  The  solution  in 


BORAX  199 

water  is  used  as  an  eye  wash.  It  is  also  illegally  used  as  a 
preservative  in  meats,  fish,  milk,  butter,  and  other  food 
products. 

195.  Boron.     The  element  boron  is  never  found  in  nature 
in  the  free  state.     It  is  a  greenish  brown,  amorphous  powder, 
without  taste  or  odor.     As  it  has  no  common  uses,  it  is  not 
prepared  in  large  quantities.     Borax  and  boric  acid  are  the 
only  important  compounds  of  boron. 

196.  Test  for  Boric  Acid.     To  test  for  boric  acid  warm 
the  substance  with  sulphuric  acid  and  alcohol  and  ignite 
the  alcohol  vapor.     If   boric  acid  or  borax  is  present,  the 
flame  will  have  a  green  color.     If  a  sample  of  food  is  to  be 
tested  for  boric  acid,  it  must  first  be  moistened  with  a  strong 
solution  of  sodium  hydroxide  (NaOH),  and  burned.     The 
ash  is  then  tested  for  boric  acid  as  above. 


EXERCISES 

Ex.  115.  What  is  the  composition  of  quartz  and  ordinary  sand? 
What  is  the  chemical  name  and  formula  for  quartz,  or  silica  ?  Discuss 
the  occurrence  of  silica  in  nature.  What  valuable  gems  are  composed 
of  silicon  dioxide  ?  What  is  infusorial  earth  ?  What  uses  are  made  of 
it?  If  possible  collect  some  specimens  of  equisetum  and  examine 
them.  Burn  some  of  them  and  note  the  amount  of  sand  in  the  ash. 
How  is  the  element  silicon  prepared?  How  widely  is  the  element 
distributed  in  nature?  What  use  is  made  of  it  commercially? 

Ex.  116.  Place  a  teaspoonful  of  commercial  water  glass  in  an  evap- 
orating dish  and  dilute  it  with  about  an  ounce  of  water.  Add  some  hy- 
drochloric acid  and  note  the  gelatinous  precipitate.  What  is  this  ma- 
terial? Write  the  reaction  between  the  acid  and  the  water  glass. 
Evaporate  the  material  in  the  dish  to  dryness  and  heat  the  dish  cau- 
tiously over  the  bare  flame.  When  cool  add  water  and  examine  the 
residue.  What  is  this  substance  ?  What  reaction  took  place  when  the 
dish  was  heated  ?  How  is  water  glass  made  ? 


200  INORGANIC  CHEMISTRY 

Ex.  117.  Try  at  home  the  experiment  of  preserving  eggs  in  water 
glass.  Dilute  the  commercial  water  glass  with  nine  times  its  volume 
of  water  and  keep  the  eggs  immersed  in  the  liquid.  Cover  the  jar  or 
crock  to  prevent  evaporation.  Only  perfectly  fresh  eggs  should  be 
used.  The  eggs  will  keep  for  a  year  or  more.  What  other  uses  are 
made  of  water  glass  ?  What  is  ordinary  glass  and  how  made  ?  De- 
scribe some  of  the  different  kinds  of  glass. 

Ex.  118.  What  can  you  say  about  the  distribution  of  the  natural 
silicates?  Give  the  formulas  for  the  different  silicic  acids.  What 
are  meant  by  mixed  salts  ?  Do  the  natural  silicates  contain  more  than 
one  metal  as  a  rule  ?  How  are  the  silicates  decomposed  in  the  labora- 
tory ?  What  is  the  chemical  test  for  silica  or  a  silicate  ? 

Ex.  119.  Examine  a  crystal  of  borax.  What  is  its  chemical  name 
and  formula?  Dissolve  a  crystal  in  water.  How  does  the  solution 
feel?  Test  with  red  litmus  paper.  What  uses  are  made  of  borax? 
Why  is  it  used  in  soldering?  Should  it  be  used  as  a  food  preservative? 
What  is  boric  acid  and  how  is  it  prepared  ?  What  use  is  made  of  it  ? 

Ex.  120.  Place  a  crystal  of  borax  in  an  evaporating  dish.  Add 
a  little  sulphuric  acid  and  some  alcohol.  Warm  gently  and  ignite  the 
alcohol.  Is  a  color  imparted  to  the  flame?  How  could  the  presence 
of  borax  or  boric  acid  in  a  food  be  detected  ? 


CHAPTER  XX 
RECOGNITION   OF  SUBSTANCES 

197.  Review  of  the  Non-metals.     The  most  important  of 
the  non-metallic,  or  acid-forming,  elements  and  their  more 
familiar  compounds,  as  well  as  two  of  the  metals,  sodium 
and  calcium,  have  been  discussed  in  the  preceding  chapters. 
Before  taking  up  the  other  important  metallic  elements  it 
will  be  well  to  review  some  of  the  facts  already  learned.     In 
order  to  present  these  facts  from  a  new  viewpoint  this  re- 
view is  made  in  connection  with  a  study  of  the  tests  for  the 
recognition  of  the  non-metals  and  their  radicals.     To  avoid 
unnecessary  repetition  references  are  given  to  the  previous 
statements  of  facts,  and  to  understand  what  is  said  here  the 
reader  should  look  up  every  reference  and  reread  the  state- 
ment. 

198.  Testing   for   a   Single    Substance.    The   complete 
analysis  of  a  mixture  of  substances  is  a  very  difficult  matter 
and  requires  much  more  knowledge  of  chemistry  than  can 
be  obtained  from  the  study  of  a  brief  treatise  such  as  this  one. 
Most  of  the  substances  that  have  been  studied  are  either 
elements  or  simple  compounds,  and  it  is  possible  to  work 
out  a  scheme  for  their  recognition  that  will  not  be  too  elab- 
orate for   the   purposes    of  this  text.     To  identify  a  salt 
completely  it  is  necessary  to  investigate  the  acid  and  the 
basic  radicals  as  two  separate  problems;    but  at  this  time 
only  the  method  of  recognizing  the  acid  radical  will  be 

201 


202  INORGANIC   CHEMISTRY 

presented,  and  the  detection  of  the  basic  or  metallic  part  of 
the  salt  will  be  studied  in  Chapter  XXVIII. 

199.  Examination  of  a  Solid.  If  the  substance  under 
examination  is  an  element,  it  is  probably  carbon,  or  sulphur, 
as  these  are  the  only  familiar  non-metallic  elements  that  are 
solids'.  Carbon  may  be  recognized  by  its  black  color  (89-94) 
and  by  the  fact  that  carbon  dioxide  is  formed  when  it  burns. 
Ignite  the  substance  and  hold  over  it  a  glass  rod  which  has 
been  dipped  in  limewater  (101).  Sulphur  may  be  recog- 
nized by  its  yellow  color  (59).  Verify  by  dissolving  in  carbon 
bisulphide  and  recrystallizing  (60). 

If  the  material  is  not  one  of  the  above  elements,  place  a 
small  quantity  in  a  test  tube,  moisten  it  with  sulphuric  acid, 
warm  it  gently,  and  note  the  result. 

(a)  A  colorless  gas  may  be  given  off.     The  odor  of  sul- 
phur dioxide   indicates  that  the   substance   is   a  sulphite 
(86  and  88).     The  odor  of  hydrogen  sulphide  indicates  a 
sulphide  (87).     If  the  gas  is  odorless,  it  is  probably  carbon 
dioxide  from  a  carbonate.     Test  it  with  a  glass  rod  that  has 
been  dipped  in  limewater  (101).     A  gas  may  be  given  off 
which  is  colorless  but  which  fumes  when  breathed  upon. 
This   indicates   hydrochloric   acid   from   a   chloride    (121). 
Verify  by  dissolving  a  small  portion  of  the  original  substance 
in  water  and  adding  a  drop  of  nitric  acid  and  a  few  drops 
of  silver  nitrate  (132).     It  may  be  nitric  acid  from  a  nitrate. 
Verify  by  adding  a  bit  of  zinc  and  heating  (153),  or  by  testing 
a  water  solution  of  the  original  substance  with  ferrous  sul- 
phate and  sulphuric  acid  (149). 

(b)  A  yellow  gas  which  does  not  fume  may  be  chlorine 
from  bleaching  powder  (124) ;    in  which  case  the  gas  will 
readily  bleach  litmus  paper  or  a  bit  of  colored  cloth  or  a 
flower  (123). 


RECOGNITION  OF  SUBSTANCES  203 

(c)  No  gas  evolved  indicates  a  sulphate  (88),  a  phosphate 
(180),  a  borate  (196),  a  silicate  (191),  or  a  basic  oxide. 

(d)  The  substance  may  be  an  ammonium  salt.    Test  by 
heating  a  small  portion  with  a  solution  of  sodium  hydroxide 
and  noting  the  odor  (167). 

EXERCISES 

Ex.  121.  Obtain  samples  of  single  unknown  substances  from  the 
teacher  and  test  them  carefully  according  to  the  plan  outlined  in  this 
chapter.  Read  the  chapter  carefully  before  beginning  the  experiment. 
Look  up  all  cross  references.  The  substances  may  be  any  of  the  follow- 
ing: 

sulphur  carbon 

a  sulphide  a  carbonate 

a  sulphite  a  nitrate 

a  sulphate  a  phosphate 

a  chloride  a  borate 

an  ammonium  salt 

Make  a  careful  record  of  the  results  of  each  test. 

(Note.     The   teacher  should   make   this  chapter  the  basis  of   a 
thorough  review  of  the  preceding  chapters.) 


CHAPTER  XXI 
POTASSIUM 

200.  THE  metal  potassium  resembles  sodium  in  most  of 
its  properties.     It  is  a  soft  solid,  which  will  float  on  water. 
The  freshly  cut  surface  has  a  silvery-white  metallic  luster. 
It  acts  upon  water  even  more  energetically  than  does  sodium, 
causing  the  evolution  of  hydrogen  and  forming  potassium 
hydroxide : 

K  +  H2O  ->-  KOH  +  H. 

The  heat  evolved  by  this  reaction  is  so  great  that  it  ignites 
the  liberated  hydrogen.  Like  sodium  it  must  be  stored  in 
coal  oil  to  prevent  its  absorbing  moisture  and  oxygen  from 
the  air. 

201.  Occurrence  of  Potassium.     The  metal  is  never  found 
free,  but  its  compounds  are  widely  distributed.     Many  of 
the  rocks  from  which  soils  are  formed  contain  potassium 
compounds,  and  consequently  potassium  is  present  in  small 
quantities  in  all  soils.     Potassium  is  one  of  the  essential 
constituents  of  plant  food  and  is  always  found  in  plants. 
When  vegetable  material  is  burned,  the  potassium  remains 
in  the  ashes  as  potassium  carbonate  (K2CO3).     Formerly 
wood  ashes  were  the  principal  source  of  potassium.     The 
impure  potassium  carbonate  dissolved  from  the  wood  ashes 
is  called  potash.     Some  of  the  giant  seaweeds  that  grow 
along  the  Pacific  coast  contain  as  much  as  35  per  cent  of 

204 


POTASS  UM 


205 


their  dry  weight  of  potassium  chloride.  Much  potassium 
is  obtained  from  the  potash  deposits  of  Europe.  These 
deposits  are  made  up  of  sixteen  or  more  different  salts,  and 
the  beds,  which  are  nearly  3000  feet  thick,  were  probably 
formed  by  the  evaporation  of  sea  water. 

The  element  potassium  is  prepared  by  electrolysis  of  its 
compounds  in  the  manner  described  under  sodium  (125). 


FIG.  115.  —  Mining  potash  salts. 

202.  Potassium  Hydroxide.     Potassium  hydroxide  (KOH) 
is  a  white,  brittle  substance  resembling  sodium  hydroxide, 
and  is  prepared  by  the  same  methods  (126).     It  absorbs 
moisture  when  exposed  to  the  air  and  is  used  for  removing 
both  water  and  carbon  dioxide  from  gases.     In  chemical 
behavior  it  is  like  sodium  hydroxide,  and  as  the  latter  is 
much  cheaper  than  potassium  hydroxide  it  is  more  commonly 
used    commercially.     The    common    name    for    potassium 
hydroxide  is  caustic  potash. 

203.  Potassium  Chloride.     Potassium  chloride  (KC1)  re- 
sembles the  corresponding  sodium  compound  in  appearance 


206 


INORGANIC  CHEMISTRY 


and  chemical  behavior.  The  chloride  is  found  in  large 
quantities  in  the  European  deposits  and  is  used  as  the  start- 
ing point  in  the  production  of  most  of  the  other  potassium 
compounds.  The  crude  salt  is  sold  as  a  fertilizer  under  the 
trade  name  of  muriate  of  potash. 

204.  Potassium  Carbonate.   Potassium  carbonate  (K2CO3) 
b  commonly  prepared  from  wood  ashes.     The  ashes  are 

placed  in  a  barrel  or 
other  receptacle,  and 
water  is  poured  on 
them  and  drawn  off 
at  the  bottom.  The 
lye  thus  obtained 
contains  potassium 
carbonate,  or  potash, 
and  is  often  used  in 
making  soft  soap. 
The  refined  potas- 
sium carbonate  is 
called  pearl-ash.  It 
has  been  stated  that 
the  substance  sold 
as  potash  is  very 
often  sodium  hy- 
droxide (126). 

205.  Potassium 
Sulphate.  Potassium  sulphate  (K2SO4)  occurs  in  combina- 
tion with  other  salts  of  potassium  in  the  European  deposits. 
It  is  sold  as  a  fertilizer  under  the  name  of  sulphate  of  potash. 
It  is  also  used  in  medicine  and  in  preparing  ordinary  alum. 
206.  Potassium  Nitrate.  Potassium  nitrate  (KNO3)  is 
commonly  called  saltpeter  or,  sometimes,  niter.  When  or- 


FIG.  116.  — Leaching  potash  from  wood  ashes. 


POTASSIUM  207 

ganic  matter  containing  nitrogen  decays  in  the  presence 
of  bases,  nitrates  are  formed  (168).  Advantage  was  for- 
merly taken  of  this  fact  to  produce  saltpeter  artificially.  Ref- 
use animal  matter  was  mixed  with  earth  and  wood  ashes 
and  the  pile  was  moistened  with  liquid  manure  from  the 
stable.  After  two  or  three  years  the  nitrate  that  had  de- 
veloped in  the  pile  was  dissolved  out  with  water  and  purified. 
In  some  hot,  dry  climates  saltpeter  is  formed  in  the  soil 
near  the  villages  in  quantities  sufficient  to  be  extracted  on 
a  commercial  scale.  At  the  present  time,  however,  most  of 
the  potassium  nitrate  is  made  by  treating  a  hot  solution  of 
sodium  nitrate  with  potassium  chloride. 

NaNO3  +  KC1  ->-  KNO3  +  NaCl. 

Potassium  nitrate  is  a  white  solid  which  occurs  in  long  slender 
crystals.  It  gives  off  oxygen  readily  when  heated  and  is, 
therefore,  a  good  oxidizing  agent.  It  is  used  to  some  extent 
in  medicine  and  in  the  preservation  of  meat,  but  its  principal 
use  is  in  the  manufacture  of  black  gunpowder. 

207.  Gunpowder  is  a  mixture  of  potassium  nitrate  (75 
per  cent),  charcoal  (15  per  cent),  and  sulphur  (10  per  cent). 
The  ingredients  are  moistened  with  water  and  thoroughly 
mixed  by  grinding,  and  the  mixture  is  then  dried.  When 
gunpowder  burns  in  a  closed  space,  a  large  amount  of  gas 
is  suddenly  formed.  One  gram  of  powder  yields  280  cc. 
of  gas,  and  the  heat  produced  causes  a  great  expansion  of 
the  gas.  The  reaction  is  approximately  as  follows : 

2  KNO3  +  3  C  +  S  ->-  3  CO2  +  2  N  +  K2S. 

The  explosion  is  due  to  the  suddenness  with  which  the  gases 
are  generated  and  the  heat  is  developed.  Smokeless  powder 
(314)  has  now  replaced  black  gunpowder  in  warfare. 


208  INORGANIC  CHEMISTRY 

208.  Potassium  Chlorate.     Potassium  chlorate   (KC1O3) 
was  used  in  the  preparation  of  oxygen  (28).     At  high  tem- 
peratures it  decomposes  into  oxygen  and  potassium  chloride  : 

KC1O3  ->-  KC1  +  3  O. 

Potassium  chlorate  forms  flat  white  crystals  and  tastes 
like  saltpeter.  It  is  used  to  prepare  oxygen  and  in  the 
manufacture  of  fireworks  and  matches.  In  the  form  of 
chlorate  of  potash  tablets  it  is  used  as  a  remedy  for  sore 
throat.  It  is  prepared  by  the  electrolysis  of  a  hot  solution 
of  potassium  chloride : 

KC1  +  3  H2O  -»-  KC1O3  +  6  H. 

209.  Potassium   Cyanide.      Potassium    cyanide    (KCN) 
is  a  white  solid  which  smells  like  bitter  almonds.     It  is 
extremely  poisonous.     It  is  used  in  photography  and  in 
extracting  gold  from  its  ores.     When  acted  upon  by  sul- 
phuric acid,  it  yields  a  gas  having  the  formula  HCN  : 

2  KCN  +  H2SO4  ->-  K2SO4  +  2  HCN. 

This  gas  (HCN)  is  called  hydrocyanic  acid.  Its  solution 
in  water  is  known  as  prussic  acid.  Hydrocyanic  acid  is  a 
deadly  poison  and  is  sometimes  used  in  fumigating  trees 
to  kill  scale  insects  and  also  in  the  fumigation  of  greenhouses. 
It  must  be  used  with  extreme  care. 

210.  Test  for  Potassium  Compounds.    A  beautiful  violet 
color  imparted  to  the  Bunsen  flame  is  the  test  for  potassium 
compounds.     This  test  is  easily  applied  to  the  pure  com- 
pounds, but  if  sodium  is  present  the  yellow  sodium  flame 
hides  the  violet  color  of-  the  potassium.     If  the  flame  is 
viewed  through  a  piece  of  blue  (cobalt)  glass  or  through  a 
thin  layer  of  indigo  solution,  the  violet  color  can  readily 
be  seen,  while  the  yellow  color  is  not  transmitted. 


POTASSIUM  209 


EXERCISES 

Ex.  122.  What  substance  previously  studied  does  potassium  re- 
semble ?  How  does  it  react  with  water  ?  Is  it  more  or  less  energetic 
than  sodium  ?  Discuss  the  occurrence  of  potassium  in  nature.  What 
is  potash?  What  compound  of  potassium  is  found  in  wood  ashes? 
What  is  the  principal  source  of  potassium  compounds  at  the  present 
time  ?  Try  the  flame  test  on  a  potassium  salt.  What  is  the  result  ? 

Ex.  123.  What  is  caustic  potash?  Allow  a  small  piece  of  potas- 
sium hydroxide  to  remain  exposed  to  the  air  on  a  watch  glass.  What 
happens?  What  substance  with  which  you  are  familiar  does  potas- 
sium chloride  resemble  in  appearance  and  chemical  behavior  ?  Where 
is  crude  potassium  chloride  obtained  ?  What  use  is  made  of  it  chemi- 
cally ?  By  what  common  name  is  it  generally  known  ? 

Ex.  124.  Place  some  wood  ashes  on  a  filter  and  pour  on  a  little 
water.  How  does  the  liquid  which  runs  through  the  filter  feel  when 
rubbed  between  the  fingers?  Evaporate  the  filtrate.  What  is  the 
composition  of  the  residue  ?  Have  you  ever  seen  soft  soap  made  with 
lye  from  wood  ashes  ?  Do  wood  ashes  which  have  been  exposed  to  the 
weather  contain  much  potash  ? 

Ex.  125.  What  is  the  chemical  composition  of  saltpeter?  The 
chemical  name  and  formula  ?  How  was  it  formerly  produced  ?  How 
is  it  produced  at  the  present  time  ?  For  what  is  it  used  ?  How  is 
black  gunpowder,  or  blasting  powder,  made?  What  causes  the  ex- 
plosion when  gunpowder  is  ignited  ?  What  is  the  probable  reaction  ? 

Ex.  126.  What  is-  the  formula  of  potassium  chlorate?  What 
changes  does  it  undergo  when  heated  at  a  high  temperature  ?  Have 
ready  half  a  teaspoonful  of  potassium  chlorate  and  a  like  quantity 
of  manganese  dioxide  on  separate  papers.  Place  the  chlorate  in  a  dry 
test  tube  and  heat  cautiously  until  the  chlorate  is  melted.  Test  with 
a  glowing  splint  for  oxygen.  If  not  heated  too  strongly,  no  oxygen 
will  be  evolved.  Remove  the  flame  and  at  once  drop  the  manganese 
dioxide  into  the  melted  chlorate  and  test  for  oxygen.  Why  is  the  man- 
ganese dioxide  used  with  potassium  chlorate  in  making  oxygen  ?  Does 
the  manganese  dioxide  undergo  any  change  ? 


EV.  CHBM.  — 14 


CHAPTER  XXII 
MAGNESIUM  AND   ZINC 

MAGNESIUM 

211.  Occurrence  of  Magnesium.     Magnesium  is  widely 
distributed  and  ranks  close  to  calcium  in  amount.     The  stone 
known  as  dolomite,  or  magnesian  limestone  (CaCO3  •  MgCOs) 
is    well    known.     Some    mountain    ranges    are    largely    of 
dolomite  and  beds  of  it  cover  thousands   of  square  miles 
in  the  Mississippi  Valley.     Magnesite  (MgCOs)  occurs  fre- 
quently.    Magnesium  carbonate  is  usually  found  to  some 
extent  in  all  limestones.     Magnesium  is  found  in  sea  water, 
in  many  mineral  waters,  and  in  several  of  the  European 
potash  salts.     It  is  a  component  of  serpentine,  talc  soap- 
stone,  asbestos,  meerschaum,  and  some  other  silicates. 

212.  Magnesium  is  a  lustrous,  silvery-white  metal  having 
a  specific  gravity  of  only  1.75.     It  is -produced  from  its 
compounds  by  electrolysis.     It  is  ductile,  and  when  hot 
may  be  drawn  into  wire  or  ribbon,  the  latter  being  a  common 
commercial  form.     It  burns  with  a  dazzling  white  light. 
Magnesium  powder  is  an  ingredient  of  photographic  flash- 
light powders,  in  which  the  magnesium  is  mixed  with  about 
twice  its  own  weight  of  powdered  potassium  chlorate. 

213.  Magnesium  oxide  (MgO)  is  the  white  bulky  powder 
formed  when  magnesium  burns.     It  is  usually  manufac- 
tured by  heating  the  carbonate,  just  as  lime  is  made  from 
limestone.     It  is  often  called  magnesia,  or  calcined  magnesia. 

210 


MAGNESIUM  211 

It  is  used  in  medicine  for  certain  forms  of  dyspepsia  and  as 
an  antidote  for  poisoning  by  mineral  acids.  It  does  not  form 
the  hydroxide  as  readily  as  calcium  oxide  does,  and  the  lime 
made  from  magnesium  limestone  is  not  so  desirable  for 
building  purposes  as  that  from  calcium  limestone. 

214.  Magnesium  sulphate    (MgS<V7H2O)   is  the   salt 
known  as  Epsom  salts.     It  was  first  recognized  in  the  mineral 
spring  at  Epsom,  England.     It  is  used  in  medicine  as  a 
purgative ;  also  as  a  coating  for  cotton  cloth,  and  in  dyeing. 

215.  Magnesium  chloride   (MgCl2)   is   even   more  deli- 
quescent than  calcium  chloride.     When  exposed  to  the  air, 
it  soon  absorbs  sufficient  moisture  to  dissolve  itself.     It 
is  present  in  small  quantities  in  all  natural  deposits  of  common 
salt,  and  the  tendency  of  table  salt  to  become  moist  and 
cake  is  due  to  the  presence  of  magnesium  chloride.     A 
small  amount  of  sodium  bicarbonate  added  to  salt  will  pre- 
vent caking.    Starch  is  sometimes  used  for  the  same  purpose. 

216.  Test  for  Magnesium  Compounds.     Make  a  small 
cavity  in  a  piece  of  charcoal  and  fill  it  with  the  substance  to 
be  tested.    Moisten  with  water  and  heat  strongly  in  the  blow- 
pipe flame  (Fig.  125).    Cool,  add  a  drop  of  cobalt  nitrate  solu- 
tion, and  heat  again.    Cool  and  examine.    Magnesium  com- 
pounds leave  a  pink  or  pale  flesh-colored   residue  in  the 
charcoal. 

ZINC 

217.  Preparation  of  Zinc.     Zinc  is  found  as  zinc  blende 
(ZnS)  and  smithsonite  (ZnCO3).     From  the  carbonate  ore, 
zinc  oxide  (ZnO)  is  obtained  by  heating.     From  zinc  blende, 
the  oxide  is  produced  by  roasting  the  ore  which  removes  the 
sulphur  and  leaves  the  oxide : 

ZnS  +  3  O  ->-  ZnO  +  SO2. 


212  INORGANIC  CHEMISTRY 

The  oxide  is  then  reduced  by  heating  with  powdered  coal : 

ZnO  4-  C  ->•  Zn  +  CO. 

This  method  of  extracting  zinc  from  its  ores  should  be 
carefully  considered.  The  ores  of  most  metals  consist  of 
the  carbonates,  oxides,  or  sulphides ;  and  the  method  of 
handling  them  is  in  general  the  same  as  that  described  for 
zinc.  In  the  case  of  the  other  metals  only  the  forms  of  the 
furnaces  and  other  details  vary.  The  art  of  extracting  metals 
from  their  ores  is  called  metallurgy.  The  metallurgy  of 
zinc  involves  the  roasting  of  the  ores  to  produce  the  oxide, 
which  is  then  reduced  with  carbon. 

218.  Pure  zinc  (Zn)  is  a  bluish  white  metal  with  a  specific 
gravity  of  7.1.     It  can  be  rolled  into  thin  malleable  sheets. 
When  melted  and  poured  into  water,  it  forms  thin  flakes 
and  in  this  condition  is  called  mossy  zinc.    Sheet  zinc  is  used 
as  a  lining  for  tanks  and  sinks  and  to  protect  floors  beneath 
stoves.     In  sticks  or  plates  it  is  used  in  electric  batteries. 
Iron  dipped  into  melted  zinc  becomes  coated  with  zinc  and 
is  called  galvanized  iron.    The  zinc  protects  the  iron  and 
prevents  rusting.     About  two  thirds  of  the  zinc  produced  is 
used  in  this  way.     In  the  laboratory  it  is  used  to  prepare 
hydrogen.     It  is  used  also  in  the   manufacture  of  brass, 
German  silver,  and  other  alloys  (255). 

219.  Zinc   oxide    (ZnO)  is  a  white  powder  obtained  by 
roasting  the  carbonate,  or  by  burning  the  metal.    It  is  com- 
monly known  as  zinc  white.     It  is  used  as  a  pigment  in  white 
paints  and  has  the  advantage  over  white  lead  of  not  darkening 
from  exposure  to  hydrogen  sulphide,  as  zinc  sulphide  is  white, 
while  lead  sulphide  is  black.    Zinc  white,  however,  has  only 
three  fourths  the  covering  power  of  white  lead.     Zinc  oxide 
is  used  as  a  filler  in  the  rubber  of  automobile  tires.     It  is 
also  a  constituent  of  zinc  ointment. 


ZINC  213 

220.  Other  Zinc  Compounds.     Zinc  chloride  (ZnCl2)  is 
a  white  deliquescent  solid.    The  aqueous  solution  is  used 
for  cleaning  metal  surfaces  before  soldering.     The  largest 
use  of  the  chloride  is  in  wood  preservation.     Zinc  sulphate 
(ZnSCX  •  7  H2O),  commonly  known  as  white  vitriol,  is  used 
in  medicine  and  in  the  dyeing  and  printing  of  cloth. 

221.  Testing  for  Zinc  Compounds.     (1)  Zinc  is  the  only 
common  metal  that  forms  a  white  sulphide  that  is  insoluble 
in  water.     If  the  substance  is  not  soluble  in  water,  dissolve 
in  hydrochloric  acid,   neutralize  the  acid  with   ammonia 
water,  and  add  hydrogen  sulphide.     A  white  precipitate 
indicates  zinc.     (2)  Fill  a  small  cavity  in  a  piece  of  char- 
coal with  the  substance.     Moisten  it  with  water  and  heat  it 
strongly  in  the  blowpipe  flame.     Cool  it  and  moisten  it  with 
a  drop  of  cobalt  nitrate  solution,  then  heat  it  again.     Cool 
and  examine.     Zinc  compounds  leave  a  green  incrustation. 

EXERCISES 

Ex.  127.  Ignite  a  short  piece  of  magnesium  ribbon  and  note  how 
it  burns.  What  is  the  white  compound  formed?  What  use  is  made 
of  metallic  magnesium?  Discuss  the  occurrence  of  magnesium  in 
nature.  What  is  the  most  abundant  compound  of  magnesium  ?  What 
is  calcined  magnesia?  Is  magnesium  lime  as  valuable  for  building 
as  the  calcium  lime  ?  What  is  the  common  name  for  magnesium  sul- 
phate ?  What  is  the  effect  of  the  presence  of  a  small  quantity  of  mag- 
nesium chloride  in  table  salt  ?  What  is  meant  by*  the  statement  that 
magnesium  chloride  is  very  deliquescent  ? 

Ex.  128.     Test  a  sample  of  a  magnesium  compound  (216).    Result? 

Ex.  129.  Give  the  properties  of  zinc.  For  what  is  it  used  ?  How 
does  it  react  with  dilute  acid  ?  Write  reaction  for  preparation  of  hy- 
drogen from  zinc  and  sulphuric  acid.  How  is  zinc  separated  from  its 
ores?  Give  reactions  in  the  preparation  of  zinc  from  the  sulphide. 
How  is  zinc  oxide  prepared  ?  How  used  ?  Test  a  sample  of  zinc  oxide 
according  to  paragraph  221.  Name  articles  at  home  that  contain  zinc. 


CHAPTER  XXIII 
ALUMINUM 

222.  ALUMINUM  is  a  bluish  white  metal  with  a  specific 
gravity  of  2.6,  which  is  about  one  third  that  of  iron.  It  is 
ductile  and  malleable  and  can  be  readily  drawn  into  a  wire 
or  pressed  into  thin  sheets.  Aluminum  does  not  change  in 
the  air,  and  this  property,  combined  with  its  low  specific 


FIG.  117.  —  Lightweight  camp  cooking  outfit  of  aluminum. 

gravity,  makes  it  useful  in  the  manufacture  of  articles  in 
which  lightness  is  important.  Its  attractive  appearance  has 
led  to  its  extensive  use  as  an  ornamental  metal.  It  is  ex- 
tensively used  for  the  manufacture  of  cooking  utensils.  The 
powdered  metal  is  used  in  making  aluminum  paint.  It  is  a 
good  conductor  of  electricity  and  is  coming  into  use  in  elec- 
tric work  as  a  substitute  for  copper,  especially  in  long-dis- 
tance wires.  A  small  quantity  of  aluminum  added  to  cast 

214 


ALUMINUM  215 

iron  prevents  the  formation  of  bubbles  and  air  holes.  The 
metal  is  trivalent  and  readily  displaces  hydrogen  from  hy- 
drochloric acid  : 


Nitric  acid  and  dilute  sulphuric  acid  act  upon  it  very  slowly. 
Concentrated  sulphuric  acid  dissolves  it,  forming  the  sulphate 
and  sulphur  dioxide.  The  metal  also  dissolves  in  strong 
alkalies.  Acids  and  alkalies  should  be  avoided  in  using 
cooking  vessels  made  of  aluminum. 

223.  Occurrence.     Aluminum  forms  7  per  cent  of  the 
earth's  crust,  and  next  to  oxygen  and  silicon  it  is  the  most 
abundant  element.     As  the  silicate  it  is  found  in  feldspar, 
mica,  and  clay.     As  the  oxide  (A12O3),  it  occurs  in  corundum 
and  emery,  which  are  used  as  abrasives.     The  sapphire,  the 
ruby,  the  oriental  topaz,  and  the  amethyst  are  aluminum 
oxide  colored  by  traces  of  impurities.     Cryolite,  a  fluoride 
of  aluminum  and  sodium  (Na3AlF6),  is  an  important  com- 
pound.   Aluminum  occurs  also  as  the  hydrated  oxide  called 
bauxite  (A12O3  •  3  H2O)  . 

224.  Preparation.     Although  aluminum  is  very  abundant 
in  nature,  it  is  never  found  in  the  free  state.     The  cost  of 
the  earlier  methods 

of  separating  it  from 
its  ores  was  so  great 
that  until  recent 
years  it  was  almost 
a  curiosity.  Since 
aluminum  is  a 

FIG.  118.  —  Electrolytic  production  of  aluminum. 

stronger       reducing 

agent  than  carbon,  the  metal  cannot  be  prepared  by  the 

method  used  for  zinc.     It  was  formerly  made  by  heating 


216  INORGANIC  CHEMISTRY 

the  chloride  with  metallic  potassium.  The  method  now 
used  (Fig.  118)  was  discovered  in  1886  by  Charles  W.  Hall, 
an  American  youth,  just  out  of  college  and  only  twenty- 
two  years  of  age.  Hall's  method  consists  in  passing  an 
electric  current  through  a  mass  of  molten  cryolite  to  which 
bauxite  has  been  added.  Under  these  conditions  the 
bauxite  is  decomposed  into  aluminum  and  oxygen.  This 
process  has  reduced  the  price  of  the  metal  from  $90  a  pound 
in  1886  to  about  twenty  cents  a  pound  at  present.  If  a 
cheap  method  could  be  discovered  to  prepare  it  from  ordi- 
nary clay,  the  metal  could  be  put  to  many  new  uses. 

225.  Aluminum  sulphate  (A12(SO4)3- 18  H2O)  is  a  white 
crystalline   solid,  readily  soluble  in  water.     It    is  used  in 
purifying  water  and  sewage,  as  a  mordant  for  fixing  dye- 
stuffs  on  fabrics,  and  as  a  sizing  material  in  the  manufac- 
ture of  paper. 

226.  Ordinary  Alum.     When  solutions  of  aluminum  sul- 
phate and  potassium  sulphate  are  mixed  and  evaporated, 
transparent,    colorless,    glassy    crystals    are    formed.     This 
solid  is  alum  and  has  the  composition  represented  by  the 
formula  KA1(SO4)2   12  H2O.     Alum  is  very  soluble  in  water, 
and  the  solution  has  an  acid  reaction  and  a  sweetish,  puckery 
taste.     When  heated  it  loses  its  water  of  crystallization  and 
some  sulphuric  acid  and  falls  into  a  white  powder  or  porous 
mass  known  as  burnt  alum,  which  is  used  in  medicine. 

227.  Other  Alums.     It  will  be  noted  that  alum  is  com- 
posed of  a  univalent  metal  (potassium)  and  a  trivalent  metal 
(aluminum)  combined  with  the  sulphuric  acid  radical.     Any 
univalent  atom  may  be  substituted  for  potassium,  and  any 
trivalent  atom  (as  the  iron  or  chromium  atom)  may  take 
the  place  of  aluminum.     No  matter  what  the  combination 
may  be,  the  crystalline  form,  the  water  of  crystallization, 


ALUMINUM 


217 


the  acid  reaction,  and  the  puckery  taste  are  the  same.  The 
following  are  the  better  known  alums : 

KA1(SO4)2  •  12  H2O  —  potassium  alum ; 
NH4A1(SO4)2  •  12  H2O  —  ammonium  alum ; 
NH4Fe(SO4)2  •  12  H2O  —  iron  alum ; 
KCr(SO4)2  •  12  H2O  —  chrome  alum. 

The  aluminum  alums  are  used  in  the  dyeing  industry,  in  the 
manufacture  of  paper,  and,  improperly,  in  baking  powder 
(426).  They  are  also  used  in  fireproofing  wood  and  cloth. 
Chrome  alum  is  used  in  the  tanning  industry  and  as  a 
hardener  in  the  fixing  bath  used  in  photography. 

228.  Clay,  Pottery,  Porcelain.  Clay  is  an  impure 
aluminum  silicate  formed  by  the  action  of  carbon  dioxide 
and  water  on  the 
feldspars,  during  the 
weathering  of  granite 
rocks.  The  products 
of  the  decomposition 
are  chiefly  an  in- 
soluble aluminum 
silicate  and  a  soluble 
alkaline  silicate.  The 
latter  is  largely 
washed  away.  The 
aluminum  silicate  is 
pure  clay  or  kaolin 
(H4Al2Si204).  Pure 
kaolin  is  a  white, 
powdery  mass.  Or- 
dinary clay  contains  many  impurities,  such  as  quartz  and 
compounds  of  iron,  calcium,  and  magnesium. 


FIG.  119.  —  The  interior  of  a  pottery  kiln. 


218 


INORGANIC   CHEMISTRY 


All  kinds  of  clay  form  a  stiff  plastic  mass  which  can  be 
molded  into  any  shape.  When  dried  it  shrinks  consider- 
ably, and  when  strongly  heated  it  shrinks  still  further  and 
forms  an  infusible  mass  which  is  not  attacked  by  water  or 

acids,  and  which  can 
no  longer  be  made 
into  a  paste  with 
water.  In  this  way 
bricks,  pottery,  and 
porcelain  are  made. 
The  red  color  in 
bricks  and  common 
pottery  is  due  to 
iron  in  the  clay. 

As  burned  clay  is 
very  porous,  pottery 
is  generally  glazed 
by  throwing  salt  into 
the  oven  in  which 

FIG.  120.  — Brick  making  in  the  old  way,  India. 

pottery  is  being 

fired.  The  steam  from  the  clay  decomposes  the  salt,  giving 
NaOH  and  HC1,  and  the  alkali  combines  with  some  of  the 
clay,  forming  a  fusible  silicate,  which  melts  and  covers  the 
pottery  or  brick,  and  on  cooling  becomes  a  hard  glassy  film. 

For  porcelain  pure  kaolin  mixed  with  feldspar  is  used. 
After  the  porcelain  is  fired,  it  is  glazed  by  being  covered  with 
a  thin  cream  of  powdered  feldspar  and  water  and  heated 
to  a  white  heat.  The  feldspar  melts  and  penetrates  the 
porcelain,  forming  a  thoroughly  adherent  glaze. 

229.  Ultramarine  is  a  deep  blue  material  used  as  a  paint 
pigment,  for  laundry  blue,  in  making  blue  tinted  paper, 
and  in  correcting  the  yellow  shade  of  linen,  starch,  sugar, 


ALUMINUM  219 

and  paper  stock.  It  is  made  by  heating  together  kaolin, 
sodium  carbonate,  sulphur,  and  charcoal.  Formerly  it  was 
prepared  by  powdering  the  blue  mineral,  lapis  lazuli. 

230.  Test  for  Aluminum.  When  an  aluminum  compound 
is  strongly  heated  in  a  blowpipe  flame,  and  the  resulting 
white  mass  is  moistened  with  a  drop  of  cobalt  nitrate  solu- 
tion and  again  heated,  it  becomes  sky  blue. 

EXERCISES 

Ex.  130.  Give  the  general  properties  of  aluminum.  Does  it  rust 
or  tarnish?  How  does  it  compare  with  iron  in  weight?  For  what 
is  it  used  ?  Why  should  acids  and  alkalies  be  avoided  in  using  cooking 
vessels  made  of  aluminum?  How  does  aluminum  occur  in  nature? 
How  is  the  metal  prepared  ?  Why  can  it  not  be  reduced  with  carbon 
as  in  the  case  of  zinc?  What  effect  did  Hall's  discovery  have  on  the 
price  of  aluminum  ?  What  aluminum  articles  can  you  find  at  home  ? 

Ex.  131.  Dissolve  about  ten  grams  of  aluminum  sulphate  in  the 
least  possible  amount  of  boiling  water.  Dissolve  3  grams  of  potassium 
sulphate  in  the  same  way.  Mix  the  clear,  hot,  saturated  solutions 
in  a  shallow  dish,  and  allow  the  mixture  to  cool  undisturbed.  Re- 
move and  examine  the  best  crystals  which  form.  Are  they  aluminum 
sulphate  ?  Potassium  sulphate  ?  Has  a  new  compound  been  formed  ? 
What  is  this  substance?  Test  to  prove  that  these  crystals  contain 
potassium,  aluminum,  and  the  sulphate  radical.  Give  the  formula  for 
ordinary  alum.  Test  a  solution  of  alum  with  blue  litmus  paper.  Give 
names  and  formulas  of  three  other  alums.  Mention  some  uses  of  the 
alums. 

Ex.  132.  What  is  clay  and  how  formed  ?  What  is  the  appearance 
of  pure  kaolin  ?  Why  are  some  clays  colored  ?  Work  some  clay  into 
a  plastic  mass  with  water.  Heat  a  piece  of  this  mass  to  a  high  temper- 
ature. How  has  the  heat  affected  the  plasticity  of  the  clay?  How 
are  bricks  and  common  pottery  made?  What  is  meant  by  glazing 
the  pottery  ?  From  what  is  porcelain  made  ?  How  is  it  glazed  ? 

Ex.  133.  What  is  ultramarine  and  how  is  it  made?  For  what  is 
it  used  ?  How  was  it  formerly  prepared  ?  Test  a  crystal  of  alum  for 
aluminum  according  to  paragraph  230.  What  is  the  result  ? 


CHAPTER  XXIV 


IRON 

231.   IRON  (Fe)  is  undoubtedly  the  most  useful  of  all  the 
metals.     It  rarely  occurs  in  the  free  state,  but  as  it  is  easily 

prepared  from  its  ores 
it  has  been  known 
from  the  early  ages. 
The  principal  ores  of 
iron  are  the  oxides, 
hematite  (Fe2O3)  and 
magnetite  (Fe3O4), 
and  the  carbonate 
(FeCO3).  Iron  in  the 
metallic  state  has  been 
found  in  meteors. 

232.   Extraction     of 
Iron    from    Its    Ores. 


chemical     process 


FIG.  121.  -Mining  iron  ore,  Minnesota. 

of  obtaining  iron  from  its  ores  is  a  very  simple  one.  What- 
ever ore  is  used,  it  is  first  converted  into  the  oxide  by 
roasting,  if  it  is  not  already  in  the  form  of  the  oxide  (217), 
It  is  then  reduced  in  a  blast  furnace  by  carbon  in  the  form 
of  coke  or  hard  coal.  The  carbon  removes  the  oxygen  from 
the  oxide.  The  blast  furnace  (Fig.  122)  is  from  25  to  90  feet 
high  and  from  15  to  18  feet  wide  in  the  widest  part.  Alter- 
nate layers  of  ore  and  fuel  are  introduced  at  the  top  of  the 

220 


IRON 


221 


Coke. 

ft  Iron  Ore. 
o  Lime5tone. 

D/vpj  of 
flelted  Iron. 


furnace.  Since  many  ores  of  iron  contain  earthy  impurities, 
limestone  is  always  placed  in  the  furnace  with  the  iron  and 
coke.  This  combines  with 
the  earthy  materials  to 
form  slag,  which  is  some- 
what similar  to  glass.  The 
molten  iron,  being  the 
heavier  liquid,  sinks  to 
the  bottom  and  is  drawn 
off  and  cast  into  bars 
about  three  feet  long  and 
six  inches  thick,  which  are 
known  as  pigs.  The  slag 
is  sometimes  used  in  the 
manufacture  of  Portland 
cement. 

233.  Cast    Iron.      The 
pig  iron  drawn  off  from 
the  furnace  is  always  im- 
pure,     containing     some 
phosphorus,    silicon,    sul- 
phur, and  carbon.     It  is 
brittle  and  easily  melted, 
and  is  used  for  casting, 
being  known  as  cast  iron. 

234.  Wrought  Iron. 
When    practically    all    of 
the  impurities  are  removed 
from  iron,  it  is  no  longer 
brittle.     It  becomes  mal- 
leable and  at  a  red  or  white  heat  it  can  be  hammered  or 
pressed  into  any  desired  shape.     It  is  now  known  as  wrought 


A  Drops  of 
tlcKcd  Slag. 

A.rtgter/6/ 
on  Convf/or 


FIG.  122.  — A  bkst  furnace. 


222 


INORGANIC  CHEMISTRY 


iron.     It  can  also  be  welded;    that  is,  two  pieces  of  the 
metal  can  be  united  when  hammered  or  rolled  together. 

235.  Steel  is  iron  that  contains  from  0.8  to  2.5  per  cent 
of  carbon.     Steel  can  be  forged  like  wrought  iron.     A  very 

important  property  of 
steel  is  its  power  of 
being  tempered,  or 
rendered  hard  or  soft 
at  will.  When  heated 
to  redness  and  sud- 
denly plunged  into 
cold  water,  it  is  ren- 
dered very  hard  and 
brittle.  If  heated  and 
slowly  cooled,  it  is 
made  soft,  and  by 
regulating  the  tem- 
perature at  which  it 
is  tempered,  almost 

any  degree  ^of  hardness,  toughness,  or  elasticity  may  be 

obtained. 

236.  Basic  Slag.     In  the  manufacture  of  steel  from  iron 
containing  phosphorus  the  converter  is  lined  with  dolomite 
(211),  which  absorbs  the  phosphoric  oxide  produced  during 
the  process,  and  forms  a  basic  calcium  phosphate.     When 
the  lining  has   absorbed  all  the  phosphorus  it   can   take 
up,  it  is  removed,  pulverized,  and  sold  as  a  fertilizer  under 
the  name  of  basic  slag,  or  Thomas  phosphate.     Phosphorus 
makes  steel  brittle ;    hence  the  necessity  for  removing  it. 

237.  Rusting  of  Iron.     All  kinds  of  iron  oxidize  readily 
in  moist  air,  even  at  ordinary  temperatures.     To  protect 
the  iron  from  the  air  and  moisture  and  thus  from  rusting, 


FIG.  123.  —  Casting  pig  iron. 


IRON  223 

it  is  covered  by  a  coat  of  paint,  or  it  is  galvanized  (218), 
tinned,  or  nickel-plated. 

238.  Iron  Has  Two  Valences.     One  atom  of  iron  may 
hold  two  or  three  atoms  of  a  univalent  element  in  combina- 
tion.    In  other  words,  iron  may  be  bivalent  or  trivalent, 
according   to    chemical    conditions.     Thus    there    are    two 

(chlorides,  FeCl2  and  FeCl3;  two  nitrates,  Fe(NO3)2  and 
Fe(NO3)3;  two  sulphates,  FeSO4  and  Fe2(SO4)3.  The  com- 
pounds in  which  iron  appears  to  be  bivalent  are  called  ferrous 
compounds ;  for  example,  ferrous  chloride  and  ferrous  nitrate. 
The  compounds  of  trivalent  iron  are  called  ferric  com- 
pounds ;  for  example,  ferric  chloride  and  ferric  sulphate. 

239.  Change  of  Ferrous  to  Ferric  Compounds.     Ferrous 
compounds   are   changed  to  ferric  compounds  by   contact 
with  air,  and  oxidizing  agents,  such  as  nitric  acid.     When, 
for  instance,  ferrous  hydroxide  (Fe(OH)2)  is  exposed  to  air 
while  suspended  in  water,  it  slowly  changes  to  ferric  hy- 
droxide (Fe(OH)s) : 

2  Fe(OH)2  +  H2O  +  O  ^  2  Fe(OH)3. 

So,  also,  when  ferrous  chloride  is  left  standing  in  a  solution 
of  hydrochloric  acid,  it  changes  to  ferric  chloride,  and  the 
change  is  rapidly  effected  by  boiling  with  a  little  nitric  acid, 
which  gives  up  oxygen  : 

2  FeCl2  +  2  HC1  +  O  -»-  2  FeCl3 '+  H2O. 

240.  Ferrous  sulphate  (FeSO4-7H2O)  is  the  compound 
commonly  known  as  copperas  or  green  vitriol.     It  is  formed 
by  the  action  of  sulphuric  acid  on  iron.     It  crystallizes  in 
pale  green  crystals.     It  is  used  as  a  purifier  of  water,  as 
a  disinfectant,  as  a  reagent  for  killing  weeds,  in  the  dyeing 
industry,  and  in  the  manufacture  of  writing  ink. 


224  INORGANIC  CHEMISTRY 

241.  Inks.     The  common  black  writing  inks  are  made  by 
treating  a  solution  of  ferrous  sulphate  with  a  solution  of  tannic 
acid  obtained  from  nutgalls.     A  little  gum  arabic  is  usually 
added,  and  a  preservative  to  prevent  the  ink  from  molding. 

242.  Sulphides   of   Iron.     When   iron   and   sulphur   are 
heated  together,  they  unite  to  form  ferrous  sulphide  (FeS). 
It  is  a  black  substance  which  is  used  in  the  laboratory  to 
prepare  hydrogen  sulphide.     A   sulphide  having  the  for- 
mula FeS2  is  abundantly  found  in  nature  and  is  known  as 
iron  pyrites.     It  is  a  yellow  crystallized  substance  sometimes 
called  fool's  gold.     When  strongly  heated,  the  sulphur  is 
oxidized  to  sulphur  dioxide,  and  the  iron  is  left  in  the  form  of 
the  oxide.     Iron  pyrites  is  commonly  used  as  a  source  of 
sulphur  in  the  manufacture  of  sulphuric  acid  (84). 

243.  Iron   compounds    are   very   widely   distributed    in 
nature.     All   soils  contain  small  quantities  of  iron.     The 
yellow  and  red  color  of  clays  are  due  to  the  presence  of  iron, 
as  are  also  the  colors  of  many  sandstones.    Iron  is  found  in 
plant  and  animal  tissues  in  minute  traces.     The  formation 
of  the  green  coloring  matter  of  plants  (chlorophyll)  is  de- 
pendent upon  the  presence  of  iron.     The  blood  of  animals 
contains  traces  of  iron.     In  fact,  neither  plants  nor  animals 
can  live  without  iron,  although  the  amount  needed  by  them 
is  exceedingly  small. 

244.  Test  for  Iron.     Tannic  acid  or  an  infusion  of  nut- 
galls  forms  a  blue -black  color  and  a  very  finely  divided 
precipitate,  which  remains  suspended  in  the  liquid. 

EXERCISES 

Ex.  134.  What  are  the  more  common  ores  of  iron  ?  What  can  be 
said  about  the  usefulness  of  iron  ?  Does  it  ever  occur  in  the  free  state  ? 
Is  its  use  by  man  of  recent  or  ancient  origin?  How  is  iron  extracted 


IRON  225 

from  its  ores  ?  What  is  pig  iron  ?  Cast  iron  ?  What  is  the  principal 
difference  between  cast  iron  and  wrought  iron?  What  is  meant  by 
welding  ?  What  is  the  purest  common  form  of  iron  ?  In  what  marked 
way  does  steel  differ  from  wrought  iron  ?  Visit  a  blacksmith  shop  and 
ask  the  smith  to  illustrate  the  tempering  of  steel. 

Ex.  135.  Why  is  the  presence  of  phosphorus  in  steel  objectionable  ? 
How  is  the  phosphorus  removed  in  making  steel  ?  What  is  basic  slag  ? 
j  Dissolve  a  little  basic  slag  in  nitric  acid  and  test  for  phosphorus  with 
molybdate  reagent. 

Ex.  136.  What  causes  the  rusting  of  iron?  Will  iron  rust  if  per- 
fectly dry?  How  may  it  be  protected  to  prevent  rusting?  What 
compounds  does  iron  make  with  sulphur  ?  What  is  fool's  gold  ? 

Ex.  137.  Dissolve  a  small  amount  of  iron  in  hydrochloric  acid. 
Divide  the  solution  into  two  parts  and  to  one  add  ammonium  hy- 
droxide until  strongly  alkaline.  Filter.  Explain  the  change  in  color 
of  the  precipitate  when  exposed  to  the  air.  Write  the  reaction.  To 
the  second  part  of  the  above  solution  add  a  little  hydrogen  peroxide. 
Explain  the  effect  of  the  peroxide  on  the  solution.  Add  ammonium 
hydroxide  in  excess  as  above.  How  does  the  precipitate  compare  with 
that  from  the  first  solution?  What  two  classes  of  compounds  does 
iron  form  ? 

Ex.  138.  What  is  the  chemical  name  and  formula  of  copperas? 
How  is  it  made  ?  For  what  is  it  used  ?  Add  a  little  tannic  acid  to  a 
solution  of  copperas.  What  happens?  What  is  the  test  for  iron? 
Discuss  the  distribution  of  iron  compounds  in  nature.  Is  iron  necessary 
to  plant  and  animal  life  ?  How  many  articles  can  you  find  at  home  that 
are  made  of  iron  ? 


EV.  CHEM.  — 15 


CHAPTER  XXV 


LEAD 

245.   Occurrence  and  Metallurgy  of  Lead.    Lead  is  found 
in  nature  principally  as  the  sulphide  (PbS),  known  as  galena, 

or  galenite,  a  heavy  black 
mineral  which  crystallizes 
in  cubes  having  a  bright 
metallic  luster.  In  the 
process  of  obtaining  lead 
from  the  ore,  the  ore  is 
first  roasted  in  order  that 
a  part  of  the  sulphide  may 
be  converted  into  the 
oxide  and  sulphate : 


PbS  +  3  O 
PbS  +  4O 


PbO  +  S02, 
PbS04. 


FiG.  124.  —  Galena. 

Air  is  then  excluded  from  the  furnace,  whereupon  the  sul- 
phide reacts  with  the  oxide  and  sulphate  as  follows  : 

2  PbO  +  PbS  ->•  3  Pb  +  S02, 
PbSO4  +  PbS  ->-  2  Pb  +  2  SO2. 

246.  Properties  and  Use  of  Lead.  Lead  is  the  heaviest 
of  the  cheaper  metals,  having  a  specific  gravity  of  11.34. 
It  has  a  bright  white  luster  when  freshly  cut  but  tarnishes 
quickly  in  the  air.  The  many  uses  of  this  metal  depend 

226 


LEAD  227 

chiefly  upon  its  low  melting  point,  its  great  density,  and  its 
softness.  It  is  so  soft  that  it  can  be  pressed  through  a  die 
into  the  form  of  tubing,  which  is  used  by  plumbers  to  make 
waste  pipes  for  sinks  and  sometimes  even  for  water  pipes. 
Sheet  lead  is  used  for  roofing  and  for  lining  tanks.  Lead 
foil  forms  an  air-tight  package  for  tea.  Mixed  with  20  per 
cent  of  antimony  it  furnishes  type  metal ;  with  0.5  per  cent 
of  arsenic  it  is  used  for  small  shot ;  and  equal  parts  of  lead 
and  tin  form  solder.  Lead  dissolves  easily  in  nitric  acid, 
forming  the  nitrate  Pb(NO3)2.  Hydrochloric  and  sulphuric 
acids  have  little  effect  on  it ;  hence  its  use  in.  lining  the 
chambers  and  pans  used  in  manufacturing  sulphuric  acid, 

247.  Lead  in  Drinking  Water.     Lead  pipes   are   some- 
times used  to  convey  drinking  water,  but  there  is  some  danger 
in  this  use  of  lead  unless  the  water  is  hard.     Hard  water 
will  generally  cover  lead  with  a  coating  of  carbonate  which  is 
insoluble  and  which  protects  the  metal  from  further  action. 
Soft  water,  however,  dissolves  some  of  the  lead,  which  when 
thus  dissolved  in  water,  acts  as  a  poison.     Cases  of  lead 
poisoning  produced  by  water  which  has  passed  through  lead 
pipes  are  not  uncommon.     Lead  acts  as  a  cumulative  poison, 
so  that  minute  quantities  taken    daily  for  some  weeks  or 
months  may  finally  produce  fatal  results. 

248.  Oxides  of  Lead.     Litharge,  or  lead  monoxide  (PbO), 
is  readily  formed  by  exposing  lead  at  a  red.  heat  to  the  action 
of  air.     It  is  a  buff-colored  substance  and  is  used  in  the  prep- 
aration of  boiled  linseed  oil  and  in  the  manufacture  of  glass 
and  enamels.     Red  lead,  or  lead  tetroxide  (Pb3O4),  is  formed 
by  heating  the  monoxide  to  about  350  degrees  C.     It  is  used 
in  making  flint  glass  and  in  the  common  red  paint  used  on 
iron  work.     Mixed  with  linseed  oil  it  is  used  in  plumbing 
and  gas  fitting  to  make  tight  joints. 


228 


INORGANIC  CHEMISTRY 


249.  Sugar  of  lead  (PlXQHaC^)  is  a  soluble  salt  pre- 
pared by  dissolving  litharge  in  vinegar  or  acetic  acid.     Sugar 
of  lead  is  sometimes  used  in  hair  dyes,  but  its  use  in  this  way 
is  considered  dangerous,  as  it  is  likely  to  produce  paralysis. 

250.  White  lead  is  a  basic  carbonate  of  lead,  having 
the  composition  2  PbCO3  -Pb(OH)2.     It  is  one  of  the  most 
important  compounds  of  lead  and  is  used  in  the  prepara- 
tion of  paints.     It  is  prepared  by  the  action  of  carbon  dioxide 
on  the  oxide  and  acetate  of  lead.     As  a  pigment  for  paints 
it  has  an  advantage  over  all  others  in  its  much  greater  opacity 
and  covering  power.     It  has  the  disadvantage  that  it  is 
readily  blackened  by  hydrogen  sulphide,  and  it  is  poisonous 
to  the  workmen  who  handle  it.     House  painters  are  some- 
times subject  to  a  painful  disease  known  as  lead  colic,  which 
is  caused  by  the  slow  absorption  of  small  particles  of  white 
lead  into  the  system.     White  lead  is  often  adulterated  with 
chalk  or  barium  sulphate.     It  is  being  replaced  for  some 
purposes  by  zinc  white  (219),  which  is  not  discolored  by 
hydrogen  sulphide. 

251.  Lead  arsenate   (Pbs^sO^)   is   a  white  substance 
usually  sold  in  the  form  of  a  paste  or  a  powder.     It  is  used 

for  poisoning  potato  bugs  and 
as  an  insecticide  for  use  in 
spraying  trees  and  shrubs. 
It  is  less  soluble  than  Paris 
green  and  adheres  more 
firmly  to  the  plant,  and  is  not 
so  likely  to  injure  the  plant. 
252.  Tests  for  Lead.  If  a 
compound  of  lead  is  mixed 
with  sodium  carbonate  and 

FIG.  125.  —  Testing  for  lead  with  blow-      i         ,    j  •  £     i_  i 

pipe.  heated  on  a  piece  or  charcoal 


LEAD  229 

in  the  inner  flame  of  a  blowpipe  (Fig.  125),  a  small  bead  of 
metallic  lead  is  obtained,  and  the  softness  of  the  bead  indi- 
cates the  nature  of  the  metal.  A  solution  of  potassium 
chromate  added  to  a  solution  containing  lead  gives  a  pre- 
cipitate of  chrome  yellow.  Hydrogen  sulphide  gives  a  black 
precipitate  of  lead  sulphide  (PbS). 

EXERCISES 

Ex.  139.  What  is  the  principal  ore  of  lead  ?  How  is  lead  prepared 
from  the  ore  ?  Examine  a  piece  of  freshly  cut  lead  and  state  its  prop- 
erties. What  happens  to  lead  when  heated?  When  exposed  to  the 
air?  Is  it  easily  melted  and  tarnished?  What  physical  properties 
adapt  it  for  its  extensive  use?  What  are  some  of  the  uses  made  of 
lead  ?  Why  is  it  used  in  lining  the  chambers  and  pans  in  making  sul- 
phuric acid  ?  Is  there  any  lead  in  lead  pencils  ?  Why  should  lead  pipes 
be  avoided  for  carrying  drinking  water?  Which  dissolves  more  lead, 
hard  or  soft  water  ? 

Ex.  140.  What  is  the  composition  of  the  red  lead  used  in  paint? 
What  is  litharge  and  for  what  is  it  used  ?  What  is  sugar  of  lead  ?  Test 
a  sample  of  hair  dye  from  the  local  drug  store  by  adding  a  little  hydro- 
gen sulphide.  A  black  precipitate  indicates  the  presence  of  lead. 

Ex.  141.  Test  a  lead  compound  according  to  paragraph  252.  What 
is  the  result  ?  The  same  test  may  be  applied  to  the  precipitate  from 
the  hair  dye  to  confirm  the  test  for  lead. 

Ex.  142.  What  is  the  substance  known  as  white  lead  ?  How  is  it 
manufactured?  For  what  is  it  used?  What  advantage  and  what 
disadvantage  does  it  have  for  use  in  paints  ?  Test  a  sample  of  paint 
for  the  presence  of  lead.  Is  white  lead  often  adulterated?  What 
advantage  does  zinc  oxide  have  over  white  lead?  Why  does  white 
lead  paint  become  blackened  ? 


CHAPTER  XXVI 


COPPER 

253.  COPPER  is,  industrially,  one  of f  the  most  important 
of  the  metallic  elements.  It  occurs  free  in  nature  and  for 
this  reason  has,  together  with  silver  and  gold,  been  known 
from  a  very  early  period.  It  is  characterized  by  its  reddish 
color.  This  color,  however,  is  seen  only  in  fresh  surfaces 
since  the  metal  soon  becomes  covered  with  a  film  of  oxide, 
sulphide,  or  carbonate.  Copper  is  flexible,  hard,  and  tough, 
and  can  readily  be  drawn  into  wire  or  rolled  into  very  thin 
sheets.  Next  to  silver  it  is  the  best-known  conductor  of 
heat  and  electricity.  Hydrochloric  acid  and  cold  sulphuric 

acid  have  little  effect  upon  cop- 
per. It  dissolves  in  nitric  acid, 
forming  the  nitrate  (Cu(NO3)2) 
and  various  oxides  of  nitrogen 
(143).  With  hot  sulphuric 
acid  it  forms  the  sulphate 
(CuSC>4)  and  sulphur  dioxide. 
The  most  common  ore  of  cop- 
per is  copper  pyrites  (CuFeS2) . 
Copper  is  precipitated  from 
solutions  of  its  salts  by  iron,  zinc,  and  some  other  metals, 
as  can  be  shown  by  dipping  a  piece  of  bright  iron  or  steel 
into  a  solution  of  copper  sulphate  (Fig.  126).  Copper  will 
immediately  be  deposited  as  a  thin,  red  coating  upon  the 

230 


FIG.  126.  —  Copper  deposited  on  a 
knife  blade. 


COPPER  231 

iron,  and  a  corresponding  amount  of  the  iron  will  go  into 
solution  to  replace  the  copper. 

CuSO4  +  Fe  ->-  FeSO4  +  Cu. 

254.  Uses  of  Copper.    Next  to  iron,  copper  is  the  most 
useful  metal.     Enormous  quantities  of  copper  wire  are  used 
in  operating  the  telegraph,  the  telephone,  the  electric  rail- 
way, and  the  electric  light.     Sheet   copper  is  made  into 
household  utensils,  boilers,  and  stills.     Copper  bolts,  nails, 
and  rivets  are  used  in  ships  because  copper  rust  does  not 
destroy  wood  as  iron  rust  does.     It  is  used  for  ornamental 
and  artistic  purposes,  and  in  the  printing  trade  for  engraving 
and  electrotyping. 

255.  Alloys.     Some   metals    intermix   when   melted   to- 
gether and  when  cooled  form  a  metal-like  substance  which 
has  properties  somewhat  different  from  either  of  the  separate 
metals.     Such  a  mixture  of  two  or  more  metals  is  called  an 
alloy.     Copper  is  a  constituent  part  of  many  of  the  most 
important  alloys.    The  following  are  some  common  alloys : 

Brass  ....     63% -73%    copper,  27%-37%    zinc 
Bronze     .     .     .     70% -95%    copper,     l%-25%   zinc, 

19&-18%   tin 

German  silver    .     50% -60%  copper,  20%  zinc, 

20%-30%   nickel  - 

Gun  metal     .     .     90%  copper,  10%  tin 

Silver  coin     .     .     10%  copper,  90%  silver 

Nickel  coin    .     .     75%  copper,  25%  nickel 

Bell  metal     .     .75%  copper,  25%  zinc. 

256.  Copper-plating   and   Electrotyping.     Copper  is  de- 
posited from  a  solution  of  its  salts  by  the  electric  current. 


232  INORGANIC   CHEMISTRY 

This  fact  is  utilized  in  copper-plating.  The  object  to  be 
plated  is  connected  with  the  negative  pole  of  a  battery  and 
hung  in  a  solution  of  copper  sulphate.  The  other  pole  is 
connected  with  a  bar  of  copper  which  is  also  immersed  in  the 
solution.  As  the  current  passes  through  the  solution,  the 
copper  salt  is  decomposed,  and  the  copper  is  deposited  on 
the  object  to  be  plated.  A  like  amount  of  copper  is  dis- 
solved from  the  bar  connected  with  the  positive  pole. 

Books  are  often  printed  from  electrotype  plates.  These 
are  made  by  first  taking  an  impression  of  the  type  in  wax. 
The  inside  of  the  mold  thus  formed  is  dusted  over  with 
powdered  graphite  in  order  to  make  it  conduct  electricity. 
The  mold  is  connected  with  the  negative  pole  of  the  battery 
and  suspended  in  a  solution  of  copper  sulphate.  As  the  cur- 
rent passes,  copper  is  deposited  upon  the  mold  in  a  cohe- 
rent film,  and  a  perfect  copy  of  the  type  is  obtained.  The 
sheet  is  strengthened  by  filling  in  the  under  surface  with 
melted  lead.  For  the  daily  newspaper  this  process  is  too 
slow  and  the  printing  is  done  from  stereotype  plates,  which 
are  made  by  pouring  melted  stereotype  metal,  consisting  of 
lead,  antimony,  and  tin,  into  a  paper  pulp  cast  of  the  type. 
This  process  gives  a  printing  surface  much  inferior  to  the 
electrotype  plate. 

257.  Oxides  of  Copper.  When  copper  is  heated  to  red- 
ness in  the  presence  of  plenty  of  air  or  oxygen,  a  black  oxide  is 
formed  having  the  formula,  CuO.  This  compound  is  called 
cupric  oxide.  In  the  absence  of  sufficient  oxygen  to  form 
the  cupric  oxide,  another  oxide  having  a  bright  red  color  is 
produced.  This  is  cuprous  oxide,  Cu2O.  Two  series  of  salts 
(cupric  and  cuprous)  of  copper  can  be  prepared  corresponding 
to  these  two  oxides,  but  only  the  cupric  compounds  are  of 
any  great  commercial  importance, 


COPPER  233 

258.  Copper  sulphate,  CuSO4,  is  the  best  known  of  the 
salts   of  copper.     It  crystallizes   from   water   in   beautiful 
blue  crystals  having  the  formula  CuSO  4  •  5  H2O,  commonly 
called  blue  vitriol  or  bluestone.     When  heated,  the  crystals 
lose  water  and   the   mass   becomes   white.     The   colorless 
substance  becomes  blue  again  in  contact  with  water.     It  is 
used  in  galvanic  batteries,  in  copper-plating,  and  as  a  start- 
ing point  for  the  formation  of  various  compounds  of  copper. 
All  copper  compounds  are  poisonous  to  plants  and  animals. 

259.  Copper   hydroxide,  Cu(OH)2,  is   formed  as  an  in- 
soluble precipitate  when  any  soluble  hydroxide  is  added  to 
a  solution  of  copper  sulphate  or  to  any  other  soluble  salt  of 
copper : 

CuSO4  +  Ca(OH)2  -^  Cu(OH)2  +  CaSO4. 

It  is  light  blue  in  color.  Copper  hydroxide  formed  according 
to  the  above  reaction  from  copper  sulphate  and  slaked  lime 
is  known  as  Bordeaux  mixture  and  is  used  in  spraying  plants 
for  the  control  of  certain  fungous  diseases.  Bordeaux  mix- 
ture alone  is  a  fungicide  merely  and  has  little  poisonous  ef- 
fect on  insects.  To  make  it  an  insecticide  as  well  arsenate 
of  lead  (251)  is  commonly  added  to  the  mixture.  Ammonia 
water  when  added  to  a  solution  of  copper  sulphate  first 
precipitates  copper  hydroxide  and  then  redissolves  it,  form- 
ing a  deep  blue  solution.  This  preparation  has  been  used 
as  a  fungicide  under  the  name  of  ammoniacal  copper  sulphate, 
but  its  use  is  largely  superseded  by  Bordeaux  mixture. 

260.  Paris  green  is  a  complex  compound  of  copper  with 
arsenious  acid  and  acetic  acid.     It  is  a  brilliant  green  material 
sometimes  called  emerald  green.    It  is  used  in  paint  making, 
but  more  largely  for  the  destruction  of  potato  bugs  and  other 
injurious  insects.     It  is  slightly  soluble  and  if  used  in  too 


234  INORGANIC  CHEMISTRY 

large  quantities  kills  the  plant  as  well  as  the  insects.  To 
render  it  more  insoluble  lime  is  sometimes  added  to  it  (183). 
261.  Tests  for  Copper.  The  salts  of  copper  have  either 
blue  or  green  colors.  Ammonia  water  added  to  a  solution 
of  a  copper  salt  produces  a  pale  blue  precipitate,  which  redis- 
solves  in  an  excess  of  ammonia  water,  yielding  a  beautiful 
blue  solution.  A  piece  of  clean  iron  or  steel  dipped  into  a 
solution  of  a  salt  of  copper  quickly  becomes  covered  with  a 
red  layer  of  metallic  copper.  This  is  a  conclusive  test. 

EXERCISES 

Ex.  143.  Examine  a  piece  of  copper  and  state  its  obvious  physical 
properties.  Is  copper  a  good  conductor  of  heat?  Of  electricity?  Is 
it  flexible,  malleable,  and  ductile  ?  What  happens  to  it  when  heated  ? 
How  is  copper  found  in  nature  ?  Why  has  it  been  known  for  so  long  ? 
Mention  some  of  the  principal  uses  for  copper. 

Ex.  144.  Dissolve  a  little  copper  sulphate  in  water  and  place  a 
bright  nail  or  the  blade  of  a  knife  in  the  solution.  What  happens? 
Write  the  reaction.  Try  the  same  experiment  with  a  piece  of  zinc. 
This  experiment  may  be  used  as  a  test  for  copper. 

Ex.  145.  What  is  meant  by  an  alloy  ?  Name  some  of  the  common 
alloys.  Of  what  is  brass  composed  ?  Test  a  piece  of  brass  for  copper. 
Explain  how  copper-plating  and  electrotyping  are  conducted.  What 
is  meant  by  stereotyping  ? 

Ex.  146.  Examine  some  crystals  of  copper  sulphate.  What  is 
the  formula  ?  Give  the  common  names.  Heat  a  crystal  in  a  test  tube. 
What  happens  ?  Continue  heating  until  no  more  water  escapes.  What 
is  the  color  of  the  residue  ?  When  cool,add  a  few  drops  of  water.  What 
change  takes  place  ?  What  are  some  of  the  uses  of  copper  sulphate  ? 

Ex.  147.  Add  limewater  to  a  solution  of  copper  sulphate.  What  is 
the  precipitate?  Write  the  reaction.  What  name  is  given  to  this 
mixture  and  for  what  is  it  used  ?  Add  a  few  drops  of  ammonia  water 
to  a  solution  of  copper  sulphate.  What  happens  ?  Add  an  excess  of 
ammonia  water.  What  change  has  taken  place?  This  reaction  is 
sometimes  used  as  a  test  for  copper. 


CHAPTER  XXVH 
SILVER 

262.  SILVER  has  been  known  from  the  earliest  times,  as  it 
occurs  free  in  nature.    Most  of  the  silver  now  used,  however, 
comes  from  the  sulphide,  Ag2S,  which  is  found  in  many  places 
associated  with  lead  sulphide  (245).    The  manner  in  which 
silver  resists  oxidation  in  the  air,  together  with  its  brilliant 
luster  when  polished,  has  caused  it  to  be  used  in  all  ages  for 
articles  of  ornament  and  in  coinage. 

Nitric  acid  is  the  only  acid  that  easily  dissolves  silver 
when  dilute.  It  is  easily  acted  upon  by  hydrogen  sulphide 
and  many  other  compounds  of  sulphur.  Thus  silver  spoons 
become  blackened  from  contact  with  the  albumin  of  egg, 
which  contains  sulphur.  Silver  articles  in  contact  with 
rubber  become  black  for  the  same  reason.  The  blackening 
is  caused  by  the  formation  of  a  film  of  silver  sulphide  (Ag2S). 
Pure  silver  is  too  soft  for  constant  use  and  is  usually  hardened 
by  the  addition  of  a  small  amount  of  copper.  The  silver 
coins  of  the  United  States  contain  10  per  cent  of  copper. 
Silver  that  contains  7.5  per  cent  of  copper  as  do  British  silver 
coins  is  called  sterling  silver. 

263.  Silver-plating.     Metals  less  expensive  than   silver 
may  be  coated  with  pure  silver,  as  in  the  case  of  copper. 
Plated  silverware  has  the  appearance  of  solid  silver  and  does 
not  rust  so  long  as  the  silver  coating  is  intact.    The  object 
to  be  plated  is  carefully  cleaned,  is  attached  to  the  negative 

235 


236 


INORGANIC  CHEMISTRY 


pole  of  a  battery,  and  is  then  suspended  in  a  solution  of  silver 
nitrate  and  potassium  cyanide   (209).     The  positive  pole 

is  a  plate  of  pure  silver.  As  the 
silver  from  the  solution  is  de- 
posited on  the  plated  object  a 
like  amount  is  dissolved  from  the 
silver  plate.  The  deposit  of  sil- 
ver is  dull  and  is  brightened  by 
rubbing. 

264.  Silver  nitrate  (AgNO3) 
is  the  best  known  salt  of  silver. 
It  is  made  by  dissolving  silver 
in  nitric  acid.  It  is  a  white 
crystalline  solid  which  turns  dark 
if  exposed  to  light  while  in  con- 
It  is  sometimes  cast  into  small 
sticks  and  called  lunar  caustic.  It  dissolves  the  skin  and  dis- 
integrates the  flesh  if  applied  long  enough.  It  is  sometimes 
used  by  physicians  to  cauterize  sores  and  to  remove  abnormal 
growths.  It  is  used  also  in  making  indelible  ink  (Ex.  149). 

265.  Silver  chloride  (AgCl)  is  formed  when  hydrochloric 
acid  or  any  chloride  is  added  to  a  solution  of  silver  nitrate. 
Thus  formed,  it  is  a  white  curdy  solid  which  turns  violet 
in  the  light,  and  finally  black.     This  action  of  light  is  more 
intense  if  organic  matter  is  present.     Silver  chloride  dis- 
solves in  ammonia  water.     Silver  bromide  (AgBr)  and  silver 
iodide  (Agl)  are  analogous  to  the  chloride  in  their  properties 
and  methods   of  formation.     They  are  more  readily  de- 
composed by  light  than  is  the  chloride. 

266.  Photography  is  Jbased  on  the  fact  that  silver  salts, 
especially  the  bromide  and  iodide,  change  color  when  mixed 
with  organic  matter  and  exposed  to  light.     The  photograph 


FIG.  127.  —  Silver-plating. 

tact  with  organic  matter. 


SILVER 


237 


is  taken  on  a  glass  plate  or  celluloid  film,  which  is  coated  on 
one  side  with  a  thin  layer  of  gelatine  containing  the  silver 
salt.  The  plate  is  placed  in  the  camera  and  exposed.  The 
light  that  comes  from  the  object  being  photographed  changes 
the  silver  salt  in  proportion  to  its  brilliancy.  The  plate, 
however,  shows  no  change  until  it  has  been  developed.  The 
developer  is  a  reagent  that  acts  readily  on  that  part  of  the 
silver  salt  that  has  been  affected  by  the  light  and  changes 


NEGATIVE 


FIG.  128.  —  Negative  showing  reversal  of  lights  and  shadows,  and  positive  showing 
these  features  in  their  natural  form. 


it  to  the  metallic  silver,  which  remains  as  a  black  deposit. 
Where  the  intense  light  falls  upon  the  plate,  the  deposit 
is  heavier  than  where  little  or  no  light  falls.  Hence  the  dark 
parts  of  the  object  appear  light  on  the  plate,  and  the  light 
parts  appear  dark;  and  since  the  image  is  .the  reverse  of  the 
object,  the  plate  is  called  a  negative  (Fig.  128).  After  be- 
ing developed,  the  plate  is  placed  in  a  solution  of  sodium 
hyposulphite  ("hypo")  to  dissolve  out  the  unchanged  silver 
salts  and  is  then  thoroughly  washed  with  water.  The  treat- 
ment with  hypo  is  termed  fixing. 

The  print,  or  positive,  is  made  on  a  paper  that  has  a  surface 
prepared  in  much  the  same  way  as  the  plate  used  to  make  the 


238  INORGANIC  CHEMISTRY 

negative.  The  negative  is  placed  on  the  paper  and  exposed 
to  the  light  in  such  a  way  that  light  will  pass  through  the 
negative,  which  obstructs  the  light  in  proportion  to  the 
thickness  of  the  silver  deposit.  The  print,  therefore,  is  the 
reverse  of  the  negative  and  has  the  same  shading  as  the  object 
photographed.  The  print  may  be  developed,  fixed,  and 
washed  in  the  same  manner  as  the  negative. 

267.  Blue  prints  are  produced  by  the  action  of  light  on 
a  salt  of  iron.     A  solution  of  ferric  ammonium  citrate  and 
potassium  ferricyanide  is  brushed  on  a  sheet  of  paper  and 
dried  in  the  dark.     If  a  design  drawn  on  tracing  cloth,  or  a 
photographic  negative,  is  placed  over  this  paper  and  the 
two  are  exposed  to  the  sunlight,  the  sensitive  paper  turns  to 
a  brownish  color  where  the  light  penetrates  the  negative. 
Under  the  black  parts  of  the  negative  where  no  light  strikes 
it  the  paper  is  unaffected.     If,  now,  the  paper  is  washed  in 
water  the  unchanged  iron  salt  is  removed,  while  that  part 
affected  by  the  light  turns  to  a  blue  color.     The  blue  color 
is  due  to  the  formation  of  the  insoluble  salt  of  iron  known  as 
Prussian  blue.     Blue  print  paper  is  used  in  large  quantities 
by  architects,  engineers,  and  designers. 

268.  The  test  for  silver  is  the  presence  of  the  white 
curdy  precipitate  of  silver  chloride  formed  by  the  addition  of 
hydrochloric  acid  to  a  silver  salt.     This  precipitate  is  soluble 
in  ammonia  water  and  darkens  when  exposed  to  light. 

EXERCISES 

Ex.  148.  Give  the  physical  properties  of  silver.  Is  it  readily 
oxidized?  Why  does  it  turn  black  when  exposed  to  the  air?  When 
in  contact  with  egg,  or  rubber,  or  perspiration?  Dissolve  a  ten-cent 
piece  in  nitric  acid.  What  does  it  contain  besides  silver  ?  What  is  the 
percentage  composition  of  American  silver  coins?  Of  British  coins? 
What  is  meant  by  sterling  silver  ?  How  are  other  metals  silver-coated  ? 


SILVER  239 

Ex.  149.  What  is  the  name  and  formula  of  the  salt  produced  by 
the  action  of  nitric  acid  on  silver?  What  is  the  common  name  for 
it  ?  For  what  is  it  used  ?  Take  a  little  of  the  solution  of  the  coin  and 
add  ammonia  water  until  the  precipitate  which  first  forms  is  again 
dissolved.  With  a  clean  pen  write  your  name  on  a  piece  of  white  cloth 
with  this  liquid.  When  dry  press  a  hot  iron  on  the  writing.  What 
happens  ?  This  illustrates  one  method  of  making  indelible  ink. 

Ex.  150.  Dilute  some  of  the  above  solution  of  the  coin  with  water 
in  a  test  tube  and  add  a  little  common  salt.  What  happens  ?  Write 
the  reaction.  Expose  the  test  tube  and  contents  to  strong  sunlight  and 
note  what  happens.  Paint  a  piece  of  plain  white  paper  with  a  weak 
solution  of  salt  and  allow  it  to  dry.  Now  brush  it  over  with  a  solution 
of  silver  nitrate  (in  a  dark  room).  Place  a  fern  leaf  or  other  object  on 
the  paper  and  expose  it  to  the  sunlight,  using  a  pane  of  glass  to  keep  the 
leaf  pressed  against  the  paper.  What  happens  ?  How  is  this  property 
of  silver  salts  utilized  in  photography? 

Ex.  151.  (Teacher)  Expose  and  develop  a  photographic  plate  so  that 
the  class  may  watch  the  different  steps.  If  a  very  slow  plate  such  as  a 
lantern  slide  plate  is  used,  the  development  may  be  done  in  any  welU 
darkened  room,  in  case  a  regular  dark  room  is  not  available.  When  the 
negative  is  dry  make  a  print  with  any  good  developing  paper.  Use 
developers  recommended  by  the  manufacturers.  What  does  the  light 
coming  through  the  lens  do  to  the  plate  ?  What  does  the  developer  do  ? 
Why  is  the  hypo  used  ?  What  would  happen  if  the  plate  were  not  fixed  ? 
Explain  the  different  steps  in  the  production  of  the  print. 

Ex.  152.  Dissolve  1  gram  potassium  ferricyanide  in  5  cc.  water; 
in  a  separate  test  tube,  dissolve  1|  grams  ferric  ammonium  citrate  in  5 
cc.  water  and  mix  the  two  solutions.  Now  paint  a  piece  of  paper  with 
the  solution  in  a  dark  room  by  candlelight  and  let  .the  paper  dry. 
Expose  the  paper  to  the  sun's  rays  under  a  design  on  tracing  cloth,  or  a 
photographic  negative.  When  the  exposure  has  continued  long  enough 
(five  or  ten  minutes,  according  to  the  amount  of  light)  wash  the  paper. 
What  change  has  taken  place  ?  What  effect  did  the  light  have  on  the 
iron  salt  ?  Tell  about  any  blue  prints  which  you  have  seen. 

Ex.  153.  To  a  little  coin  solution  add  hydrochloric  acid.  What 
occurs?  Add  an  excess  of  strong  ammonia  water.  Results?  This 
illustrates  the  test  for  silver,  as  no  other  metal  forms  a  chloride  that  is 
insoluble  in  nitric  acid  and  water  and  is  soluble  in  ammonia  water. 


CHAPTER  XXVIII 

REVIEW  OF  THE    METALLIC    SALTS  —  RECOGNITION 
OF  THE  COMMON  METALS 

269.  IN  the  foregoing  chapters  ten  of  the  more  important 
metals  have  been  briefly  discussed.     Of  these  not  more  than 
seven  are  commonly  met  with  in  the  metallic  form ;  the  others 
are  rarely  seen  outside  of  the  chemical  laboratory.     Only 
three  or  four  of  the  metals  are  found  in  nature  in  the  free 
state ;  the  others  occur  in  the  oxides,  sulphides,  carbonates, 
or  silicates.     A  large  number  of  compounds  of  the  metals 
are  of  commercial  importance,  notably  the  salts,  and  a  few 
of  the  oxides  and  hydroxides. 

270.  Metallic  Salts.     Theoretically  at  least,  every  metal 
should  be  able  to  combine  with  every  acid  to  form  a  salt, 
and  as  there  are  many  acids  and  metals  the  possible  number 
of  salts  is  very  large.     Only  the  more  important  of  these 
salts  and  especially  those  which  are  of  more  or  less  common 
use  have  been  mentioned  in  this  text.     Descriptions  of  many 
others  will  be  found  in  the  larger  texts  on  chemistry. 

271.  Preparation   of   Salts.     There   are   several   general 
methods  which  may  be  used  for  the  preparation  of  salts. 

(1)  A  salt  may  be  formed  by  the  action  of  the  proper  acid 
on  a  metal,  an  oxide,  hydroxide,  or  carbonate : 

Zn  +  H2SO4  ->-  ZnSO4  +  2  H, 
CaO  +  2  HC1  ->-  CaCl2  +  H2O, 
KOH  +  HNO3  ->•  KNO3  +  H20, 
MgCO3  +  H2SO4  ->-  MgSO4  +  H20  +  CO2. 
240 


REVIEW  OF  THE  METALLIC   SALTS  241 

(2)  If  a  salt  is  insoluble  in  water  it  may  be  prepared  by 
precipitation.  To  a  solution  of  a  soluble  salt  of  the  metal  is 
added  a  solution  of  a  soluble  salt  of  the  desired  acid.  For 
example,  calcium  carbonate  may  be  prepared  by  adding  a 
solution  of  sodium  carbonate  to  a  solution  of  calcium  chloride, 
whereupon  the  calcium  carbonate  will  be  precipitated  : 

CaCl2  +  Na2CO3  -»-  CaCO3  +  2  NaCl. 


If  the  desired  salt  is  insoluble  in  acids,  it  may  be  precipi- 
tated by  adding  the  desired  acid  itself  in  place  of  the  salt  : 

AgNO3  +  HC1  -»-  AgCl  +  HN03. 

(3)  Some  of  the  binary  salts  may  be  formed  by  the  direct 
union  of  the  metallic  and  non-metallic  elements  : 

Fe  +  3  Cl  - 


272.  Solubility  of  Salts.  A  knowledge  of  the  solubility  in 
water  of  the  different  salts  is  of  importance  when  devising 
a  method  for  the  preparation  of  a  salt.  It  is  an  aid  also  in 
the  determination  of  the  basic  and  acid  parts  of  the  salt. 
The  solubility  of  the  salts  and  of  the  hydroxides  of  the  metals 
studied  may  be  summarized  as  follows  : 

(1)  Hydroxides  are  insoluble  except  those  of  ammonium, 
sodium,  potassium,  and  calcium. 

(2)  Nitrates  are  all  soluble. 

(3)  Chlorides  are   soluble   except   silver  chloride.    Lead 
chloride  is  slightly  soluble  in  cold  water  and  quite  soluble 
in  hot  water. 

(4)  Sulphates  are  soluble  except  those  of  lead  and  cal- 
cium.    Calcium  sulphate  is  slightly  soluble. 

(5)  Sulphides  are  insoluble  except  those  of  ammonium, 

EV.  CHEM.  —  16 


242  INORGANIC  CHEMISTRY 

sodium,  potassium,  calcium,  and  magnesium.  The  insoluble 
sulphides  can  be  divided  into  two  classes  :  (a)  Those  soluble 
in  dilute  acid,  as  lead  and  copper.  (6)  Those  insoluble  in 
dilute  acid,  as  iron,  aluminum,  and  zinc. 

(6)  Carbonates,  phosphates,  and  silicates  are  insoluble 
except  those  of  ammonium,  sodium,  and  potassium. 

273.  Recognition  of  the  Metals.  In  Chapter  XX  was 
given  a  scheme  for  the  recognition  of  the  acid  radicals  of  salts. 
Consideration  is  now  given  to  the  methods  of  recognizing 
the  basic  or  metallic  part  of  a  salt.  The  methods  given  here 
apply  only  to  single  substances,  as  the  analysis  of  a  mixture 
of  substances  calls  for  a  knowledge  of  analytical  chemistry. 
The  tests  will  be  confined  to  the  ten  of  the  more  common 
metallic  elements  studied :  sodium,  potassium,  calcium, 
magnesium,  zinc,  aluminum,  iron,  lead,  copper,  and  silver. 

(1)  If  the  substance  is  one  of  those  studied  in  connection 
with  Chapter  XX  and  the  acid  radical  has  been  determined, 
some  idea  as  to  the  metal  may  be  gained  by  comparing  with 
the  solubilities  given  above.     For  example,  if  the  acid  is 
found  to  be  carbonic  or  phosphoric  acid  and  the  substance 
dissolves  in  water,  the  base  must  be  ammonium,  sodium, 
or  potassium ;   if  the  substance  is  a  chloride  and  is  insoluble 
in  water,  it  must  be  silver  chloride.     An  insoluble  sulphate 
must  be  lead  or  calcium,  and  so  on. 

(2)  The  usual  method  of  detecting  the  metals  is  by  the 
use  of  reagents  that  precipitate  certain  groups  of  metals, 
which  may  again  be  subdivided  until  the  metal  is  traced. 
The  substance  to  be  tested  is  dissolved  in  water.     If  it  is 
not  soluble  in  pure  water  the  least  amount  of  nitric  acid 
should  be  used,  and  the  following  procedure  carried  out. 

(a)  Add  to  the  solution  a  little  hydrochloric  acid.  If 
a  precipitate  is  formed,  it  is  silver  chloride  (268),  or  lead 


RECOGNITION   OF  THE   COMMON  METALS      243 

chloride.  Add  ammonia  water,  which  will  dissolve  silver 
chloride.  Lead  chloride  if  present  is  not  dissolved  by  am- 
monia water  but  will  dissolve  if  the  liquid  is  heated.  Con- 
firm by  test  (252). 

(6)  If  no  precipitate  is  produced  by  hydrochloric  acid,  take 
half  of  the  solution  and  pass  hydrogen  sulphide  gas  through 
it.  A  precipitate  may  be  copper  sulphide  or  lead  sulphide. 
The  first  solution  may  have  been  too  dilute  for  the  lead  to 
precipitate  as  chloride.  Determine  -[which  is  present  by 
testing  original  substance  for  lead  (252)  and  copper  (261). 

(c)  If  no  precipitation  is  caused  by  hydrogen  sulphide, 
make  the  solution  alkaline  by  adding  ammonia  water.     A 
brownish  precipitate  is  iron  (244),  while  a  white  precipitate 
indicates  aluminum  (230)  or  zinc  (221). 

(d)  If  none  of  these  reagents  gives  a  precipitate,  evap- 
orate the  reserved  half  of  solution  to  a  small  bulk  and  add  a 
few  drops  of  sulphuric  acid.     A  precipitate  indicates  calcium. 

(e)  If  no  precipitate  is  produced  by  the  sulphuric  acid, 
make  the  solution  alkaline  with  ammonia  water  and  add  a 
solution    of    sodium    phosphate.     A    precipitate    indicates 
magnesium.     Confirm  by  testing  the  original  substance  (216). 

(/)  If  none  of  these  reagents  produces  a  precipitate,  the 
substance  is  a  salt  of  sodium  or  potassium.  Determine 
which  by  the  flame  test  (131  and  210). 

EXERCISE 

Ex.  154.  Obtain  from  the  teacher  samples  of  simple  chemical 
compounds  to  test  for  the  metal  or  basic  radical.  Read  this  chapter 
carefully  and  follow  the  outline  exactly.  The  metal  will  be  one  of  the 
following :  Sodium,  Potassium,  Calcium,  Magnesium,  Copper,  Silver, 
Lead,  Zinc,  Aluminum,  or  Iron.  Make  a  record  of  the  result  of  each  test. 

To  the  Teacher.  This  chapter  should  be  made  the  basis  of  a  thorough 
review  of  the  chemistry  of  the  metals. 


PART   II 
ORGANIC  AND  APPLIED  CHEMISTRY 

CHAPTER  XXIX 
COMPOUNDS   OF   CARBON   WITH   HYDROGEN 

274.  REFERENCE  has  been  made  (107)  to  the  known  exist- 
ence of  many  thousands  of  compounds  containing  carbon. 
These  compounds  are  for  the  most  part  produced  as  a  result 
of  the  vital  processes  of  plants  and  animals  ;  hence  the  study 
of  their  composition  and  properties   is  known  as  organic 
chemistry.    It  was  thought  formerly  that  none  of  these  com- 
pounds could  be  produced  artificially,  but  in  recent  years  a 
number  of  them  have  been  prepared  in  the  laboratory  without 
the  aid  of  living  things.     While  the  old  reason  for  making  a 
sharp  distinction  between  inorganic  and  organic  chemistry 
no  longer  exists,  it  is  still  convenient  to  study  the  com- 
pounds of  carbon  as  a  separate  branch  of  chemistry,  partly 
because  the  number  of  compounds  containing  it  exceeds  the 
number  of  all  other  compounds  put  together.     It  is  well  to 
remember  that  many  of  the  substances  produced  by  plants 
and  animals  have  defied  all  attempts  at  artificial  preparation, 
and  some  of  them,  perhaps,  will  never  be  so  produced. 

275.  Marsh  Gas.     When  leaves  or  other  organic  matter 
decompose  under  water,  a  gas  is  formed  which,  when  collected 
and  examined,  is  found  to  be  readily  combustible.     It  is  color- 
less and  odorless  and  about  one  half  as  heavy  as  air,  with 

244 


COMPOUNDS  OF  CARBON  WITH  HYDROGEN     245 


which  it  forms  an  explosive  mixture.  It  is  called  marsh  gas, 
or  methane.  It  has  the  formula  CH*.  It  is  the  simplest 
member  of  a  class  of  compounds  consisting  of  carbon  and 
hydrogen  in  different  propor- 
tions, to  which  the  general 
name  of  hydrocarbons  has 
been  given. 

Methane  is  the  chief  con- 
stituent of  natural  gas.  It  is 
formed  also  to  some  extent 
in  coal  mines,  and  the  ex- 
plosions occurring  in  these 
mines  are  often  due  to  a 
mixture  of  air  and  methane. 
Davy's  Safety  Lamp  (100) 
was  invented  to  prevent  these  explosions.  The  miners  call 
methane  fire  damp.  In  the  laboratory,  marsh  gas  is  pre- 
pared by  heating  a  mixture  of  sodium  acetate  and  soda-lime  : 

NaC2H302  +  NaOH  ->•  Na2CO3  +  CH4 

(The  lime  does  not  enter  into  the  reaction.) 
276.  Higher  Hydrocarbons.  More  than  one  hundred 
different  combinations  of  carbon  and  hydrogen  are  known, 
many  of  which  are  of  great  commercial  importance.  For 
convenience  in  study  these  hydrocarbons ,  are  arranged  in  a 
number  of  groups  or  series.  The  following  table  gives  the 
names  and  formulas  of  a  few  of  the  hydrocarbons  of  the 
methane  series. 


FIG.  129.  —  Collection  of  marsh  gas. 


Methane  - 

Ethane  - 

Propane  - 
Butane 

Pentane  - 


CH4 
C2H6 
C3H8 
C4H18 


Hexane     - 
Heptane    - 


Pentadecane 
Hexadecane 


246 


ORGANIC  CHEMISTRY 


The  first  four  members  are  gases  at  ordinary  tempera- 
tures. From  pentane  to  pentadecane  (Ci5H32)  they  are 
liquids  with  higher  boiling  points,  and  from  hexadecane  up- 
ward they  are  solids  with  increasingly  higher  melting  points. 
277.  Petroleum  is  the  principal  source  of  the  hydrocarbons 
of  the  methane  series.  It  is  a  thick,  greenish-brown  oil  found 

in  oil-bearing  strata  of  the 
earth.  The  chief  oil-pro- 
ducing areas  of  the  United 
States  are  in  Oklahoma, 
California,  Texas,  Illinois, 
Louisiana,  West  Virginia, 
Pennsylvania,  and  Ohio. 
Petroleum  is  pumped  from 
wells  sunk  in  the  ground, 
and  is  stored  in  large  tanks 
or  conveyed  directly  to  the 
refineries.  Sometimes  when 
the  oil  is  under  great  pres- 
sure of  gas,  the  newly  driven 
well  spouts  oil  from  the 
surface.  Such  a  well  is 
called  a  gusher  (Fig.  130). 
Petroleum  is  a  very  complex 
mixture  of  hydrocarbons, 
and  while  some  of  it  is  used 
crude  condition  as 


FIG.  130.  -A  spouting  oil  well  or  gusher. 

a  fuel,  its  principal  value  lies  in  the  fact  that  it  is  the 
source  of  many  useful  products  such  as  gasoline,  vaseline, 
and  paraffin.  The  crude  petroleum  is  placed  in  large  stills 
and  is  subjected  to  distillation.  The  portion  of  the  liquid 
that  distills  between  the  temperatures  of  70  degrees  F. 


COMPOUNDS   OF  CARBON  WITH  HYDROGEN     247 

and  150  degrees  is  called  naphtha ;  that  between  150°  and 
300°  is  kerosene;  while  that  which  distills  between  300° 
and  400°  is  used  for  lubricating  oil.  When  the  remaining 
oil  is  chilled  the  solid  constituents  separate  and  consti- 
tute ordinary  paraffin.  Naphtha  is  again  separated  into 
petroleum  ether,  gasoline,  and  benzine.  In  some  refineries 
a  semisolid  fraction  is  also  obtained  which  is  the  vaseline, 
or  petrolatum,  of  commerce. 

None  of  these  substances  is  a  single  chemical  compound, 
but  each  one  is  composed  of  several  hydrocarbons.  Gasoline 
consists  of  hydrocarbons  with  low  boiling  points,  while  paraf- 
fin contains  those  with  very  high  boiling  points. 

278.  Gasoline.     The  chief  uses  of  gasoline  depend  upon 
the  fact  that  it  is  very  volatile  and  is,  therefore,  easily  con- 
verted into  a  gas.     The  mixture  of  gasoline  vapor  and  air  is 
explosive,  and  this  quality  is  utilized  in  the  gasoline  engine. 
When  gasoline  is  used  in  heating  or  illuminating,  it  is  first 
converted  into  a  gas.     This  is  accomplished  by  heating  it 
or  by  forcing  air  through  it.    The  volatile  character  of  gaso- 
line is  also  the  cause  of  many  accidents.     It  is  to  be  noted 
that  nearly  all  the   accidents  with   gasoline   stoves  have 
been  caused  by  the  fact  that  the  gasoline  tanks  were  filled 
while  the  burner  was  lighted.     Gasoline  is  one  of  the  best 
solvents  for  fats  and  its  use  in  cleaning  depends  upon  this 
fact. 

279.  Acetylene  (C2H2)  is  a  colorless  gas  now  extensively 
used  for  illumination.     It  is  prepared  by  the  action  of  water 
on  calcium  carbide  (169) : 

CaC2  +  2  H2O  •*-  Ca(OH)2  +  C2H2. 

A  special  form  of  burner  (Fig.  131)  is  required  in  burning 
acetylene  to  prevent  the  formation  of  soot.  When  the  gas 


248 


ORGANIC  CHEMISTRY 


is  used  in  such  a  burner  the  flame  is  very  white  and  brilliant. 

Acetylene  is  readily  decomposed,  and  it  was  formerly  dan- 
gerous to  handle  when  compressed  in 
cylinders.  It  has  been  discovered 
that  if  the  cylinder  is  filled  with  a 
porous  material  like  asbestos  and  this 
material  is  saturated  with  a  com- 
pound called  acetone,  acetylene  may 
be  forced  into  the  cylinder  under  high 
pressure  with  perfect  safety.  Acety- 
lene, when  burned  with  oxygen  in  an 
apparatus  much  like  the  oxyhydrogen 
blowpipe,  makes  the  hottest  known 
flame  (2700°).  It  is  sometimes  used 
in  cutting  iron,  as  it  melts  its  way 
through  the  iron  at  the  point  of 

FIG.  131.  —  Acetylene  burner,      contact. 

EXERCISES 

Ex.  155.  Mix  thoroughly  a  teaspoonful  each  of  sodium  acetate  and 
soda-lime.  Place  in  a  test  tube,  arrange  as  in  Fig.  50,  and  heat.  Collect 
two  bottles  full  of  the  gas.  What  is  the  composition  of  this  gas? 
The  name  ?  The  reaction  ?  Ascertain  whether  the  gas  will  burn.  Fill 
a  bottle  half  full  of  the  gas  and  half  full  of  air  and  ignite  it.  Does 
this  mixture  explode  ?  Where  is  this  gas  found  in  nature  ?  What  do 
miners  call  it  ?  If  there  is  a  marsh  or  a  pond  near  the  school  where 
leaves  and  other  organic  matter  are  decomposing,  try  to  collect  some 
methane  as  shown  in  Fig.  129.  Why  is  this  gas  commonly  called 
marsh  gas  ? 

Ex.  156.  What  is  meant  by  a  hydrocarbon  ?  Are  many  combina- 
tions of  carbon  and  hydrogen  known  ?  As  the  number  of  carbon  atoms 
in  the  molecule  increases  what  effect  does  it  have  on  the  boiling  point  of 
the  hydrocarbon?  Are  the  hydrocarbons  with  the  largest  molecules 
liquids  or  solids? 


COMPOUNDS   OF  CARBON  WITH  HYDROGEN     249 


Ex.  167.  Examine  a  sample  of  crude  petroleum ;  also  samples  of 
gasoline,  kerosene,  and  lubricating  oil.  What  is  the  original  source  of 
all  these  substances  ?  What  is  the  chemical  nature  of  petroleum  ? 
Are  gasoline  and  kerosene  single  chemical  compounds?  In  which  do 
the  hydrocarbons  have  the  larger  molecules?  What  are  some  of  the 
important  uses  of  gasoline  ?  For  what  is  it  used  at  your  home  ? 

Ex.  158.  Place  some  calcium  carbide  in  an  apparatus  as  shown  in  j 
Fig.  132.  The  bulb  (B)  contains  water  and  is  fitted  with  a  stopcock  so 
that  the  water  can  be  slowly 
run  into  the  flask  (A).  When 
ready  to  collect  the  gas  allow 
the  water  to  run  into  the  flask 
a  drop  at  a  time.  Examine 
the  gas  which  is  evolved. 
What  is  its  name  and  for- 
mula? Give  its  reaction  of 
formation.  Why  must  it  be 
burned  in  a  special  burner  ? 
Are  any  houses  in  your 
neighborhood  lighted  with 
acetylene?  What  gas  is  in  the  gas  tanks  used  on  automobiles  and 
motorcycles?  What  temperature  is  obtained  where  acetylene  is 
burned  with  oxygen?  What  practical  application  is  made  of  this 
intense  heat  ? 


FIG.  132.  —  Laboratory  apparatus  for  the 
production  of  acetylene. 


CHAPTER  XXX 
ALCOHOLS 

280.  Wood  Alcohol.    When  wood  is  heated  in   closed 
retorts  in  the  manufacture  of  charcoal  (90),  a  distillate  con- 
sisting of  a  number  of  substances  is  obtained.     One  of  these 
compounds  is  wood  alcohol  (methyl  alcohol),  which*  has  the 
formula  CH3OH.     Wood  alcohol  is  a  colorless  liquid  that 
boils  at  65°  C.  and  burns  with  a  colorless  and  sootless  flame. 
It  is  a  good  solvent  for  resins  and  is  used  in  making  certain 
varnishes  and  shellacs.     It  is  burned  also  in  alcohol  lamps, 
although  its  use  for  this  purpose  and  for  varnishes  has  de- 
creased since  the  introduction  of  denatured  alcohol.     Wood 
alcohol  is  poisonous  and  it  produces  paralysis  of  the  optic 
nerve.    Many  cases  of  blindness  have  been  caused  by  the 
drinking  of  cheap  whiskies  adulterated  with  wood  alcohol, 
and  by  the  continued  inhaling  of  its  vapor. 

281.  Ordinary  alcohol,  also  known  as  grain  alcohol  and 
ethyl  alcohol,  has  the  formula  C2H5OH.     It  is  obtained  from 
the  fermentation  of  sugars.     The  fermentation  is  brought 
about  by  the  action  of  yeast.     In  the  case  of  grape  sugar 
(CeHtfOe)  the  reaction  may  be  represented  as  follows : 

C6H12O6  ->-  2  C2H5OH  +  2  CO2. 

Alcohol  is  prepared  commercially  from  substances  rich  in 
starch,  such  as  corn  or  potatoes.  The  starch  is  first  con- 
verted into  a  sugar  by  means  of  malt,  and  yeast  is  then  added. 

250 


ALCOHOLS 


251 


Water 


Yeast  is  a  microscopic  vegetable  organism,  which  during  its 
growth  produces  a  number  of  changes  resulting  in  converting 
the  sugar  into  alco- 
hol. The  resulting 
alcohol  is  separated 
from  the  fermented 
liquid  by  distillation 
(Fig.  133).  The  al- 
cohol of  commerce 
contains  about  5  per 
cent  of  water. 

Alcohol  is  a  color- 
less liquid  with  a 
characteristic,  pleas- 
ant odor.  It  boils  at 

78°    C.      It    is    Some-        FIG.  133.  —  A  stUl  for  the  production  of  alcoholic 

times  used  as  a  fuel,  liquors. 

especially  in  spirit  lamps,  as  it  burns  with  a  colorless  and 

sootless  flame.    It  burns  according  to  the  following  reaction : 

C2H5OH  +  6  O  -^  2  CO2  +  3  H2O. 

It  is  a  solvent  for  many  substances.  Pharmacists  use  it  in 
the  preparation  of  tinctures,  essences,  and  extracts.  Many 
of  the  better  grades  of  varnishes  and  shellacs  contain  ethyl 
alcohol.  When  the  term  alcohol  is  used  without  a  qualify- 
ing word,  ethyl  alcohol  is  always  meant.  When  taken  into  the 
system  in  small  quantities,  alcohol  produces  intoxication; 
in  larger  amounts  it  acts  as  a  more  positive  poison. 

282.  Alcoholic  Beverages.  Many  beverages  contain  al- 
cohol in  greater  or  smaller  quantity  (Fig.  134).  In  all  cases 
the  alcohol  is  produced  by  fermentation.  Wines  are  made 
by  the  fermentation  of  the  sugars  in  fruit  juices,  particu- 


252 


ORGANIC  CHEMISTRY 


FIG.  134.  —  The  percentage  of  alcohol  in  distilled 
liquor,  wine,  and  beer. 


larly  of  the  grape.  Wines  contain  5  to  15  per  cent  of 
alcohol.  Hard  cider  is  really  a  wine  produced  from  apple 
juice.  The  yeast  plant,  since  it  is  always  associated  with 

the  fruits,  need  not  be 
added  in  wine  making. 
Beer  is  made  by  the 
fermentation  of  malt; 
in  this  case  the  yeast  is 
added.  Beer  contains 
from  3  to  5  per  cent  of 
alcohol.  Corn,  rice, 
and  glucose  are  some- 
times used  to  replace 
part  of  the  malt. 
Whisky,  brandy,  rum,  and  gin  are  known  as  distilled 
liquors.  They  contain  from  40  to  60  per  cent  of  alcohol. 
Whisky  is  made  by  distilling  a  beer  made  from  rye,  corn,  or 
barley.  Brandy  is  maole  by  distilling  wine,  or  the  fermented 
juice  of  apples,  peaches,  cherries,  or  other  fruits.  Rum  is 
distilled  from  the  liquid  obtained  by  fermenting  molasses. 
Gin  is  an  alcoholic  liquor  flavored  with  oil  of  juniper  berries. 

283.  Denatured  alcohol  is  ethyl  alcohol,  to  which  is  added 
wood  alcohol,  benzine,  or  a  bad-smelling  compound  prepared 
by  heating  bones  and  known  as  pyridine.     These  substances 
make  its  use  for  beverages  or  medicine  impossible.     About 
four  fifths  of  the  cost  of  ordinary  alcohol  is  due  to  the  internal 
revenue  tax  imposed  by  the  government.     Denatured  alcohol 
is  tax  free,  to  encourage  its  use  in  the  arts.     The  denaturing 
in  no  way  impairs  its  value  as  a  fuel  or  for  use  in  varnishes 
and  shellacs. 

284.  Alcohols  Are  Bases.    The  formulas  for  methyl  alcohol 
(CH3OH)  and  ethyl  alcohol  (QjHsOH)  are  written  in  such 


ALCOHOLS  253 

a  way  as  to  show  the  presence  of  hydroxyl  in  the  compound. 
This  is  done  because  the  alcohols  are  all  bases  in  the  same  way 
that  ammonium  hydroxide  (NHjOH)  is  a  base,  although  the 
basic  character  of  the  alcohols  is  less  pronounced.  They 
react  with  acids  in  a  manner  similar  to  ammonium  hydroxide  : 

NH4OH  +  HC1  -*-  H2O  +  NH4C1  (ammonium  chloride) ; 
C2H5OH  +  HC1  ->-  H2O  +  C2H5C1  (ethyl  chloride). 

Methyl  and  ethyl  alcohols  are  hydroxides  made  by  re- 
placing one  hydrogen  atom  of  methane  and  ethane  with 
hydroxyl.  Similar  alcohols  can  be  prepared  corresponding 
to  the  more  complex  hydrocarbons,  but  most  of  them  are  of 
minor  importance. 

285.  Glycerin.    Just  as  there  are  inorganic  bases  with  more 
than  one  hydroxyl  group  in  the  molecule,  as,  for  example, 
Ca(OH)2  and  A1(OH)3,  so  there  are  alcohols  with  more  than 
one  hydroxyl  group.     The  most  important  of  these  is  glycerol, 
known  commercially  as  glycerin,  C3H5(OH)3.     Glycerin   is 
a  heavy,  colorless,  sirupy  liquid  with  a  sweet  taste.     It  is 
miscible  with  water  and  is  so  hygroscopic  that  it  will  absorb 
half  its  weight  of  water  from  the  moisture,  of  the  air.     It  is 
used  in  cosmetic  and  medicinal  preparations,  in  ink  rollers 
of  printers,  in  the  ink  for  rubber  stamps,  and  to  soften  leather. 
Glycerin  is  one  of  the  products  obtained  during  the  manu- 
facture of  soap  (303),  and  in  the  preparation  of  the  stearin 
used  in  making  candles. 

286.  Nitroglycerin  is  trinitrate  of  glycerin,  made  by  slowly 
adding  glycerin  to  a  mixture  of  nitric  and  sulphuric  acids : 

C3H5(OH)3  +  3  HN03  ->•  C3H5(N03)3  +  3  H2O. 

The  sulphuric  acid  does  not  take  part  in  the  reaction,  but 
causes  the  action  to  continue  by  keeping  the  mixture  dehy- 


254  ORGANIC  CHEMISTRY 

drated.  Nitroglycerin  is  a  heavy,  colorless,  oily  liquid. 
It  explodes  when  heated  to  180°  C.,  or  when  subjected  to  a 
shock.  Because  of  the  danger  in  handling  pure  nitroglycerin, 
it  is  mixed  with  some  inert,  porous  substance,  such  as 
infusorial  earth  or  wood  pulp.  This  mixture  is  called  dyna- 
mite, and  the  different  grades  are  classified  and  named  accord- 
ing to  the  percentage  of  nitroglycerin  they  contain. 

287.  Formaldehyde.  When  methyl  alcohol  is  burned  in 
a  limited  supply  of  air,  or  the  mixture  of  air  and  the  vapor  of 
methyl  alcohol  is  passed  over  heated  copper,  a  gas  is  formed 
which  is  known  as  formaldehyde  (CH2O) : 

CHsOH  +  O  -*-  CH2O  +  H2O. 

Formaldehyde  is  a  gas  with  a  stinging,  stifling  odor  which 
causes  the  eyes  to  smart.  It  is  a  powerful  germicide  and  is 
largely  used  to  disinfect  buildings  following  cases  of  conta- 
gious diseases.  It  is  more  effective  than  sulphur  dioxide  and 
has  no  bleaching  effect  (63).  An  aqueous  solution  contain- 
ing 40  per  cent  of  the  gas  is  sold  under  the  name  of  formalin. 
This  is  used  also  as  a  disinfectant,  and  for  the  treatment  of 
seed  potatoes  for  the  destruction  of  scab,  and  of  oats  and 
other  grain  to  destroy  smut.  Formaldehyde  is  used  also 
lor  the  preservation  of  anatomical  specimens  and  to  harden 
gelatin  films  in  photography.  It  is  sometimes  improperly 
'  employed  as  a  food  preservative. 

EXERCISES 

Ex.  159.  (Teacher)  Place  a  cupful  of  commercial  glucose,  com- 
mon molasses,  or  Karo  sirup,  in  a  two  quart  bottle  (A)  and  add  a 
quart  of  lukewarm  water.  Rub  a  cake  of  compressed  yeast  in  half 
a  cupful  of  water  and  add  it  to  the  mixture  in  the  bottle.  Connect 
the  large  bottle  with  a  small  bottle  (B)  containing  limewater,  as  shown 


ALCOHOLS 


255 


FIG.  135.  —  Producing  alcohol  in 
the  laboratory. 


in  Fig.  135.     Set  this  aside  in  a  warm  place  for  two  or  three  days. 

Bubbles  of  gas  will  soon  form  in  A  and  pass  into  B.     What  happens 

to  the  limewater?      What  is  the  gas 

formed  in  A  ?     After  fermentation  has 

ceased,  decant  about  half  of  the  liquid 

in  A  into  a  distilling  flask.1     Connect 

with  a  condenser  and  distill  off  10  to 

15  cc.      Compare  the  odor  with  the 

alcohol  of  the  laboratory.    Put  2  or  3  cc. 

in  an  evaporating  dish  and  test  it  with 

the  flame.     Will  it  burn? 

Ex.  160.  State  the  properties  of  ordinary  alcohol.  What  is  its 
chemical  name  ?  How  is  it  made  ?  Write  the  reaction  for  change  of  glu- 
cose to  alcohol.  Name  some  beverages  that  contain  alcohol.  What 
uses  are  made  of  alcohol?  What  is  meant  by  denatured  alcohol? 
Why  is  denatured  alcohol  so  much  cheaper  than  the  pure  alcohol? 
Does  denaturing  impair  its  value  for  use  in  the  arts  ? 

Ex.  161.  How  is  wood  alcohol  prepared?  What  is  the  chemical 
name  for  wood  alcohol  ?  For  what  is  it  used  ?  Why  is  caution  neces- 
sary in  using  it  ?  Why  are  alcohols  known  as  bases  ? 

Ex.  162.  Examine  a  sample  of  glycerin  and  give  its  properties; 
its  formula.  For  what  is  it  used  ?  What  is  the  source  of  commercial 
glycerin  ?  How  is  nitroglycerin  made  ?  Write  the  reaction.  What  is 
dynamite  ? 

Ex.  163.  Examine  a  sample  of  formaldehyde.  How  is  it  prepared  ? 
Give  its  formula.  For  what  is  it  used  ?  Why  is  it  .preferable  to  sulphur 
dioxide  for  disinfecting  after  sickness  ? 

1  Set  the  bottle  A  aside  and  keep  it  open  for  two  or  three  weeks  to  see 
whether  acetic  acid  will  develop. 


CHAPTER  XXXI 
ORGANIC   ACIDS 

288.  Acetic  Acid.  It  will  be  recalled  that  apple  juice,  upon 
standing,  undergoes  a  fermentation  that  results  in  the  forma- 
tion of  alcohol.  Hard  cider  may  contain  from  4  to  8  per  cent 
of  alcohol.  Upon  longer  standing  the  cider  becomes  very 
sour  and  is  then  called  vinegar.  The  sour  taste  of  the 
vinegar  is  due  to  the  fact  that  the  alcohol  has  been  changed 
into  a  substance  known  as  acetic  acid  (H 


C2H6OH  +  2  O  -»-  H  ••  C2H3O2  +  H2O. 

This  acid  is  the  most  familiar  member  of  a  class  of  compounds 
known  as  organic  adds.  All  of  them  resemble  the  inorganic 
acids  in  their  general  behavior,  but  are  weaker  acids.  Only 
one  of  the  hydrogen  atoms  of  acetic  acid  has  acid  properties, 
that  is,  can  be  replaced  by  a  metal  ;  and  that  fact  is  indicated 
in  the  formula  by  separating  the  replaceable  hydrogen  from 
the  rest  of  the  molecule.  This  method  of  indicating  the 
replaceable  hydrogen  atoms  of  the  organic  acids  is  used 
throughout  this  text. 

The  change  of  alcohol  into  acetic  acid  during  the  forma- 
tion of  vinegar  is  brought  about  by  the  action  of  a  species  of 
bacteria  known  as  Bacterium  aceti,  and  the  change  is  known  as 
acetic  fermentation,  which  is  evidently  an  oxidation  process. 
The  slimy  substance  sometimes  found  in*  vinegar  and  called 
mother  of  vinegar  consists  of  masses  of  these  bacteria.  Vine- 
gar contains  from  4  to  6  per  cent  of  acetic  acid. 

256 


ORGANIC  ACIDS 


257 


The  old  method  of  producing  vinegar  from  cider,  in  which 
the  fermentation  was  allowed  to  take  place  in  barrels,  re- 
quired many  weeks  or  months,  as  the  oxidation  could  take 
place  only  at  the  surface  of  the 
liquid.  In  the  method  known  as 
the  quick  vinegar  process  (Fig.  136), 
tall  barrels  are  loosely  filled  with 
beech-wood  shavings,  which  are 
then  moistened  with  old  vinegar  to 
introduce  the  bacteria.  The  cider 
or  other  liquid  containing  alcohol 
is  allowed  to  trickle  slowly  over  the 
shavings  and  is  thus  exposed  to  the 
action  of  bacteria  and  to  the  oxy- 
gen of  the  air.  By  this  process  the 
vinegar  is  produced  in  about  ten 
days.  Vinegars  are  sometimes 
made  from  wine,  and  from  fer- 
mented malt  extract  (malt  vinegar).  FIG.  136.  —  vinegar-making  by 

f  quick  process. 

White  wine  vinegar,  or  distilled  vine- 
gar, is  made  by  treating  solutions  of  pure  alcohol  by  the 
process  just  described. 

289.  Acetic  Acid  from  Wood.  Acetic  acid  is  one  of  the 
products  of  the  destructive  distillation  of  wood  (90) .  It  was 
formerly  called  "  pyroligneous  acid  "  ;  that  is,  the  acid  made 
by  heating  wood.  Much  of  the  acetic  acid  on  the  market  is 
made  in  this  way,  and  some  of  the  cheap  vinegar  is  merely 
a  4  per  cent  solution  of  this  acid. 

Acetic  acid,  when  pure,  is  a  colorless  liquid  with  a  pungent 
odor.  It  solidifies  at  17°  C.  and  is  soluble  in  all  proportions 
in  water.  With  metals  it  forms  salts,  among  the  most  im- 
portant of  which  are  sodium  acetate  (NaC2H3()2),  and  lead 

EV.  CHEM.  —  1? 


^58  ORGANIC  CHEMISTRY 

acetate  (Pb(C2H3O2)2)  commonly  called  sugar  of  lead. 
Copper  acetate  (Cu(C2H3O)2)  when  combined  with  copper 
arsenite  forms  Paris  green  (260). 

290.  Lactic  Acid.     Milk  upon  standing  gradually  becomes 
sour  because  of  the  formation  of  lactic  acid  (H-CsHsOa). 
This  acid  is  produced  by  the  action  of  lactic-acid  bacteria 
upon  milk  sugar  (310).     This  process  is  known  as  lactic  fer- 
mentation.    Lactic  acid  may  also  be  prepared  by  the  fermen- 
tation of  other  sugars,  and  as  it  is  now  of  some  industrial 
importance  it  is  produced  by  the  action  of  the  bacteria  found 
in  old  cheese,  upon   solutions  of    glucose,  or  cane  sugar. 
When  pure,  it  is  a  colorless,  sirupy  liquid  with  an  intensely 
sour  taste. 

291.  Oxalic  acid   (H2-C2O4)  exists   in  many  plants.     It 
gives  the  sour  taste   to   sour   grass   and   to   sheep   sorrel. 
It  differs  from  most  of  the  acids  so  far  studied  in  being 
a  solid  instead  of  a  liquid.     It  forms  large,  colorless  crys- 
tals   containing  two  molecules  of  water  of  crystallization 
(H2  •  C2O4  •  2  H2O) .     Oxalic  acid  is  poisonous.     Its  antidote  is 
calcium  carbonate  (chalk),  which  forms  with  it  the  insoluble 
calcium  oxalate  (CaC2O4).     Calcium  oxalate  is  found  in  the 
clovers  and  many  other  plants.     Oxalic  acid   is  useful   in 
removing  ink  and  rust  spots  from  floors  and  fabrics.     It  is 
used  also  in  cleaning  brass,  and  in  bleaching  straw  hats. 

292.  Tartaric   acid   (H2-C4H4O6)   is  the  acid  of  grapes. 
When  pure  it  forms  beautiful,  large,  prismatic  crystals  which 
are  readily  soluble  in  water.     In  grapes  it  is  found  as  acid 
potassium  tartrate   (KH-C4H4O6).      This  is  the  substance, 
commonly  called  cream  of  tartar.     When  a  solution  of  cream 
of  tartar  is  neutralized  with  sodium  hydroxide,  Rochelle  salt 
(KNaC4H4O6)  is  formed : 

KHC4H4O6  +  NaOH  +•  KNaC4H4O6  +  H2O. 


ORGANIC  ACIDS  259 

293.  Citric  acid  (H3-C6H5O7)  occurs  in  lemons,  oranges, 
and  other  citrus  fruits.   It  exists  also  in  currants,  gooseberries, 
and  cranberries.     Citric  acid  forms  large  colorless  crystals 
which  are  soluble  in  water.     Both  citric  and  tartaric  acid  are 
often  used  as  substitutes  for  lemons  in  making  cheap  lemon- 
ade and  other  acidulated  beverages.     Magnesium  citrate 
(Mg3(C6H5O7)2)  is  employed  as  a  purgative  in  medicine. 

294.  Tannic  acids,  or  tannins,  are  substances  with  an 
astringent  taste.     They  are  widely  distributed  in  the  vege- 
table kingdom.     The  principal  commercial  sources  are  the 
bark  of  the  oak  and  hemlock,  sumach,  nutgalls,  and  a  num- 
ber of  Indian  and  South  American  trees.     Tannins  occur  also 
in  smaller  quantities  in  the  leaves  of  many  plants.     Tannins 
are  used  for  tanning  leather,  in  dyeing,  and  in  making  ink. 

Ink  is  the  black  mixture  obtained  by  mixing  solutions  of 
tannin  with  iron  salts.  One  recipe  for  black  ink  is  as  follows  : 
Extract  100  grams  of  powdered  nutgalls  with  1.4  liters  of 
water,  and  add  50  grams  of  gum  arabic  and  50  grams  of  fer- 
rous sulphate.  When  the  mixture  is  exposed  to  the  air,  a 
permanent  black  color  is  developed.  A  black  or  a  blue  dye 
is  commonly  added  to  give  the  ink  a  temporary  color. 

The  operation  of  tanning,  or  the  conversion  of  animal  skin 
into  leather,  depends  on  the  formation  in  the  skin  of  an  in- 
soluble compound  of  tannin  and  the  albuminoid  matter  of 
the  skin.  The  tannin  is  derived  from  -oak  or  hemlock 
bark,  which  is  ground  to  a  coarse  powder  and  piled  in 
layers  with  the  skins  in  deep  vats.  The  vats  are  filled  with 
water,  and  the  skins  are  allowed  to  soak  for  a  few  weeks  or 
months. 

295.  Benzoic     acid     (H-C7H5O2)     and     salicylic     acid 
(H-C7H5O3)  are  both  solid,  crystalline  acids  that  are  used 
in  medicine  and  sometimes  as  preservatives  in  food.    Benzoic 


260  ORGANIC  CHEMISTRY 

acid  exists  naturally  in  gum  benzoin,  while  a  compound  of 
salicylic  acid  is  the  principal  ingredient  of  oil  of  wintergreen. 
Both  these  acids  are  now  prepared  artificially  from  coal  tar 
compounds. 

Sodium  benzoate  (NaC7H5O2),  is  frequently  used  as  a 
preservative  in  foods.  Its  use  is  unnecessary,  however,  and 
should  be  discouraged.  Sodium  salicylate  also  is  sometimes 
used  as  a  preservative.  Both  it  and  salicylic  acid  are  used  in 
medicine,  notably  in  the  treatment  of  rheumatism. 

296.  Organic  Salts,  or  Esters.  If  to  a  mixture  of  ethyl 
alcohol  and  acetic  acid  in  a  test  tube  a  little  sulphuric  acid  is 
added  and  the  whole  is  gently  heated,  a  vapor  with  a  pleas- 
ant, fragrant  odor  is  given  off.  This  body,  ethyl  acetate 
(C2H5-C2H3O2),  is  formed  by  replacing  the  acid  hydrogen  of 
acetic  acid  by  the  basic  ethyl  radical.  The  equation  is 

C2H5OH  +  H  .  C2H3O2  ->•  C2H5  -  C2H302  +  H2O. 

The  sulphuric  acid  absorbs  the  water  as  fast  as  it  is  formed 
and  permits  the  reaction  to  continue.  Such  salts  as  ethyl 
acetate,  in  which  both  the  basic  and  the  acid  parts  are  organic 
radicals,  are  called  ethereal  salts  or  esters,  the  shorter  name 
being  preferred.  Many  of  these  esters  exist  naturally  in 
fruits  and  impart  *to  them  their  characteristic  flavors.  They 
can  be  prepared  artificially  by  a  process  analogous  to  that 
discussed  for  ethyl  acetate  and  many  of  the  flavoring  extracts 
on  the  market  consist  of  such  artificially  prepared  esters. 
Oil  of  wintergreen  is  methyl  salicylate  (CH3-C7rI5O3). 
Most  of  the  oil  of  wintergreen  on  the  market  is  artificial. 

When  an  ester  is  gently  heated  with  an  alkali,  the  alkali 
salt  of  the  acid  is  formed  and  the  alcohol  is  set  free  : 


C2H3O2  +  NaOH  -»-  NaC2H3O2  +  C2H5OH. 

ethyl  acetate  sodium  acetate     ethyl  alcohol 


ORGANIC  ACIDS  261 

The  esters  are  also  decomposed  by  heating  with  steam  under 
pressure  into  the  acid  and  alcohol : 

C2H5-C2H3O2  +  H20-^C2H5OH  +  H-C2H3O2. 

ethyl  acetate  alcohol  acetic  acid 

EXERCISES 

Ex.  164.  What  gives  the  sour  taste  to  vinegar?  How  is  vinegar 
made  commercially?  What  is  meant  by  the  quick  vinegar  process? 
Write  the  reaction  for  change  of  alcohol  to  acetic  acid.  Give  the  prop- 
erties of  acetic  acid ;  the  formula.  How  is  acetic  acid  prepared  from 
wood  ?  What  was  the  old  name  for  it  ?  Make  a  four  per  cent  solution 
of  acetic  acid  and  compare  the  flavor  with  cider  vinegar.  Is  the  flavor 
of  a  good  vinegar  entirely  due  to  the  acetic  acid  ? 

Ex.  165.  What  acid  is  formed  when  milk  sours?  Can  you  prove 
that  an  acid  is  present  ?  Examine  the  laboratory  sample  of  lactic  acid. 
Add  a  drop  to  a  tablespoonful  of  water  and  taste  it. 

Ex.  166.  Examine  some  crystals  of  oxalic  acid.  Where  is  it  found 
in  nature  ?  Try  cleaning  an  old  straw  hat  with  a  solution  of  oxalic 
acid.  Rub  the  solution  on  with  a  sponge  or  a  piece  of  cloth  and  place 
the  hat  in  the  sun. 

Ex.  167.  Examine  some  cream  of  tartar.  What  is  the  source  of 
cream  of  tartar?  The  formula?  Examine  crystals  of  tartaric  acid. 
Give  its  formula.  What  is  formed  when  cream  of  tartar  is  neutralized 
with  sodium  hydroxide  ? 

Ex.  168.  To  what  acid  is  the  sour  taste  of  lemons  due?  What  is 
the  appearance  of  citric  acid  ?  In  what  other  fruits  is  it  found  ?  How 
is  cheap  lemonade  made  ? 

Ex.  169.  Examine  some  tannic  acid.  Dissolve  a  little  in  water 
and  taste  a  drop.  Does  it  have  an  astringent  taste  ?  Where  is  it  found 
in  nature  ?  Add  a  little  tannic  acid  solution  to  a  solution  of  ferric  chlo- 
ride. What  is  the  result  ?  Steep  a  little  oak  bark  in  water  and,  add  ferric 
chloride  to  the  solution.  Do  the  same  with  a  little  tea.  Have  you  any 
evidence  that  oak  bark  and  tea  contain  tannic  acid  ?  -How  is  ink  made  ? 
Why  does  it  get  darker  when  exposed  to  the  air  ?  How  is  tannic  acid 
used  in  tanning  leather  ?  Soak  a  piece  of  lean  meat  in  a  strong  solu- 
tion of  tannic  acid  for  a  few  days.  What  is  the  condition  of  the  meat  ? 


262  ORGANIC  CHEMISTRY 

Ex.  170.  Examine  bottles  of  factory-made  catsup  or  other  foods  at 
home  or  in  the  local  store  and  see  whether  any  have  stated  on  the  label 
that  sodium  benzoate  was  used  in  their  manufacture.  Do  you  think 
any  preservative  should  be  used  in  canning  vegetables  or  fruits  ? 

Ex.  171.  Place  1  cc.  each  of  alcohol  and  acetic  acid  in  a  test  tube. 
Add  2  cc.  of  sulphuric  acid  and  warm  the  mixture.  Note  the  pleasant 
odor  evolved.  What  is  this  substance  ?  What  is  the  general  name  for 
such  compounds  ?  How  are  they  sometimes  used  ? 

Ex.  172.  Place  a  little  wood  alcohol  and  some  salicylic  acid  in 
a  test  tube.  Add  sulphuric  acid  and  warm.  What  odor  is  given  off? 
What  is  the  chemical  composition  of  oil  of  wintergreen  ?  What  happens 
to  esters  when  heated  with  an  alkali  ?  When  heated  with  steam  under 
pressure  ? 


CHAPTER  XXXII 
FATS,    OILS,   AND   SOAPS 

297.  Fats  and  oils  are  the  products  of  both  vegetable 
and  animal  life.     Oils  are  liquid  fats.     The  more  common 
animal  fats  are  tallow,  lard,  and  butter.     Olive  oil,  palm  oil, 
cottonseed  oil,  and  linseed  oil  are  good  examples  of  vegetable 
fats.     These   fats    are   all    insoluble   in   water.     They   are 
soluble  in  ether,  chloroform,  carbon  bisulphide,  gasoline,  and 
benzine.     Hence  water  will  not  remove  grease  spots  from 
clothing,  but  benzine  and  other  solvents  of  fats  will. 

298.  Composition  of  Fats.     When  a  fat  is  heated  with 
steam  under  pressure  so  as  to  get  a  temperature  of  about 
200°  C.  it  is  decomposed  with  the  formation  of  glycerin  (285) 
and  one  or  more  organic  acids.     The  acids  more  commonly 
found  in  fats  are  palmitic  acid  (H  •  CieH3iO2) ;  stearic  acid 
(H-Ci8H35O2);  «and  oleic  acid    (H-Ci8H33O2).     These   and 
other  acids  found  in  fats  are  collectively  known  as  fatty  adds. 
Fats,  then,  are  evidently  esters  in  which  the  alcohol  is  glyc- 
erin and  the  acid  is  one  of  the  so-called  fatty  acids.      As 
glycerin  has  three  hydroxyl  groups,  its  ester  with  stearic  acid 
must  have  the  formula  CsHs^igHssO^?.     (Compare  with 
glycerin  nitrate  (286).)     The  hydrolysis  of  glycerin  stearate 
may  be  represented  as  follows  : 

C3H5(C18H3502)3  +  3  H2O  ^  C3H5(OH)3  +  3  H.C18H35O2. 

glycerin  stearate  glycerin  stearic  acid 

The  glycerin  of  commerce  and  many  of  the  fatty  acids  used  in 
candle  and  soap  making  are  produced  in  this  way. 

263 


264  ORGANIC  CHEMISTRY 

The  names  of  the  different  fats  are  derived  from  those  of 
the  fatty  acids  found  in  them,  by  changing  the  ic  of  the  acid 
to  in.  Thus  the  glycerin  ester  (or  fat)  of  palmitic  acid  is 
called  palmatin  (€*Hk(QftHfiQz)*) ;  of  stearic  acid  is  stearin 
(C3H5  (C18H3502)3) ;  of  oleic  acid,  olein  (C3H5.  (C18H33O2)3). 
Stearin  and  palmitin  are  solids,  while  olein  is  a  liquid.  The 
natural  fats  are  nearly  always  mixtures  of  the  different 
single  fats,  and  the  consistency  of  the  fat  depends  upon  the 
proportion  of  the  different  esters  present.  Beef  tallow  is  a 
mixture  of  stearin,  palmitin,  and  olein,  with  the  more  solid 
stearin  predominating.  Olive  oil  and  cottonseed  oil  contain 
large  proportions  of  olein  and  are  therefore  liquid. 

299.  Butter  and  Oleomargarine.  Butter  contains  from 
80  per  cent  to  85  per  cent  of  a  very  complex  fat  consisting  of 
several  of  the  glycerin  esters  with  olein  and  palmatin  pre- 
dominating. The  characteristic  flavor  of  the  butter  fat, 
however,  is  due  to  the  presence  of  about  5  per  cent  of  butyrin 
(C3H5(C4H7O2)3),  which  is  the  salt  of  butyric  acid  (H  C4H7O2). 
This  fat  occurs  only  in  butter,  and  the  methods  of  distinguish- 
ing true  from  adulterated  butter  depend  upon  this  fact. 

The  high  price  of  butter  has  led  to  the  manufacture  of 
certain  butter  substitutes.  Oleomargarine  is  made  from 
various  animal  fats,  combined  with  cottonseed,  peanut,  and 
palm  oils,  the  different  fats  being  nrxed  in  such  proportions 
as  to  give  a  substance  of  about  the  same  consistency  as  butter 
fat.  To  give  the  product  a  butter  flavor,  the  melted  fat  is 
poured  into  ripened  milk,  that  is,  milk  that  has  been  soured 
as  cream  is  in  butter  making,  and  is  then  churned.  In 
butterine  a  certain  proportion  of  butter  fat  is  added  to  impart 
the  butter  flavor. 

While  oleomargarine  is  a  valuable  food  product,  the 
temptation  to  sell  it  for  butter  has  proved  so  great  that 


FATS,   OILS,   AND  SOAPS  265 

strict  laws  regulating  its  sale  are  required.  Oleomargarine 
colored  to  resemble  butter  is  taxed  ten  cents  a  pound  by  the 
United  States  government,  and  the  sale  of  colored  oleo- 
margarine is  entirely  prohibited  in  some  states.  The  fraud- 
ulent substitution  of  other  fats  for  butter  fat  is  the  more 
reprehensible  in  view  of  the  recent  discovery  that  butter  fat 
contains  certain  growth-producing  substances,  called  vita- 
mines,  which  are  not  found  in  lard  and  vegetable  fats. 

300.  Renovated  Butter.     Much  of  the  butter  placed  on 
the  market  becomes  strong  or  rancid,  and  the  "  renovating  " 
of  this  butter  has  become  an  important   industry.     The 
butter  is  melted  and  the  curd  and  the  water  are  removed 
as  well  as  the  scum  on  the  top.     Air  is  then  forced  through 
the  melted  fat  until  the  disagreeable    odors  are  removed 
and  the  fat  is  nearly  tasteless.     The  fat  is  then  churned 
with  ripened  milk  as  in  the  case  of  oleomargarine. 

301.  Making  Solid  Fats  from  Oils.     A  comparison  of  the 
formulas  of  the  liquid  fat  olein  and  the  solid  fat  stearin  shows 
that  the  latter  contains  six  more  hydrogen  atoms  than  olein. 
By  treating  olein  with  hydrogen  in  the  presence  of  finely 
powdered  nickel,  which  acts  as  a  catalytic  agent,  it  can  be 
made  to  absorb  hydrogen  and  thus  be  changed  into  stearin. 
This  process  is  known  as  hydrogenation  of  ails.    A  number  of 
edible  lard  substitutes   are  made  by  hydrogenating  cotton- 
seed oil  until  it  has  the  consistency  of  lard. 

Hydrogenation  has  proved  of  great  value  also  in  soap 
making.  Oils  that  give  soft  soaps  can  be  converted  into 
compounds  that  yield  the  more  valuable  hard  soaps.  Fish 
oils,  which  have  objectionable  odors,  can  by  this  process 
be  deodorized  and  made  suitable  for  soap  making. 

302.  Drying  Oils.     Linseed  oil  consists  largely  of  the  fat 
having  the  formula  C3H5(Ci8H3iO2)3.    This  fat  is  linolein, 


266  ORGANIC  CHEMISTRY 


the  glycerin  salt  of  linoleic  acid  (H'CigHsiC^).  It  will  be 
noted  that  linolein  has  twelve  fewer  hydrogen  atoms  in  the 
molecule  than  stearin.  It  has  the  property  of  absorbing 
oxygen  from  the  air  and  thereby  of  being  changed  into  a  hard, 
solid  substance.  For  this  reason  linseed  oil  is  called  a  drying 
oil  and  it  is  this  property  that  makes  it  valuable  for  use  in 
paint  making.  A  few  other  oils,  for  example,  poppyseed  oil 
and  corn  oil,  have  this  property  of  drying  in  a  less  marked 
degree  than  linseed  oil. 

303.  Soaps.  All  esters  are  decomposed  when  heated  with 
the  hydroxides  of  the  alkalies.  With  stearin  and  sodium 
hydroxide  the  reaction  is 


3  NaOH->C3H5(OH)3  +  3  NaC18H3502. 

glycerin  stearate  glycerin  sodium  stearate 

Sodium  stearate  is  a  soap.  Reactions  like  the  above  may 
be  made  to  take  place  between  all  fats  and  the  hydrox- 
ides of  sodium  or  potassium,  and  in  each  case  a  soap  is 
formed.  Soaps,  therefore,  may  be  said  to  be  the  sodium 
or  potassium  salts  of  the  fatty  acids.  Sodium  soaps  are 
known  as  hard  soaps,  while  those  containing  potassium  are 
soft  soaps. 

In  soap  making  the  lye  solution  is  gradually  added  to  the 
oil  or  melted  fat,  which  is  kept  warm  and  stirred  by  jets  of 
steam.  When  the  reaction  appears  to  be  complete,  salt  is 
added  to  the  mixture  and  the  soap  separates  and  floats  on 
top,  as  it  is  insoluble  in  a  solution  of  salt.  This  process  is 
called  salting  out.  In  this  method  of  making  soap  most  of 
the  glycerin  remains  in  the  solution  with  the  salt  and  spent 
lye  and  is  hard  to  recover.  In  the  old  fashioned  homemade 
soft  soap  (Fig.  137)  the  alkali  used  is  potassium  carbonate 
obtained  by  leaching  wood  ashes.  The  potassium  is  present 


FATS,   OILS,  AND  SOAPS 


267 


in  plants  as  the  salts  of  organic  acids,  but  all  alkali  salts  of 
organic  acids  are  changed  to  carbonates  when  burned : 

-f  O  ->•  K2CO3  +  CO2. 


The   larger  soap  factories   first  hydrolyze  the  fats  with 
superheated  steam,  and    a    part    of    the    liberated    fatty 
acids  are  treated  with  so- 
dium hydroxide  to  make 
the  soap.     The    reaction 
between  an  alkali  and  a 
fat  resulting  in  the  pro- 
duction    of    a    soap    is 
known  as  saponification. 

Calcium  and  magne- 
sium salts  of  the  fatty 
acids  are  insoluble  in 
water,  and  these  insoluble 
salts  are  formed  when 
soap  is  added  to  hard 
water  (119).  As  these 
insoluble  compounds  have 
no  cleansing  power,  that 
part  of  the  soap  which 

reacts  with  the  calcium  and  magnesium  of  hard  water  is 
wasted.  The  methods  of  determining  hardness  of  water 
depend  on  the  fact  that  a  lather  is  not  produced  in  water 
until  all  of  the  calcium  and  magnesium  is  precipitated  (16). 

304.  Essential  Oils.  Many  plants  contain  so-called 
essential  or  volatile  oils  which  impart  to  them  their  char- 
acteristic taste  or  odor.  These  substances  are  not  true  oils 
and  vary  in  character  according  to  the  source.  They  are 
completely  volatilized  when  heated  and  leave  no  permanent 


FlG  137  _  Making  soft  soap  on  the  farm 


268  ORGANIC  CHEMISTRY 

greasy  residue  on  cloth  or  paper.  Oil  of  lemon,  oil  of  pepper- 
mint, and  oil  of  cedar  are  examples  of  essential  oils.  The 
odor  of  new-mown  hay  is  due  to  a  volatile  oil.  The  clovers, 
particularly  sweet  clover,  have  characteristic  essential  oils. 
These  oils  are  lost  when  the  hay  is  overcured  or  exposed  to 
leaching  rains.  Some  of  the  essential  oils  of  foods  exert  a 
favorable  influence  on  digestion  by  imparting  palatability 
to  the  food  and  stimulating  the  flow  of  the  digestive  fluids. 
Some  of  the  essential  oils  have  medicinal  value,  while  others, 
as  oil  of  bitter  almonds,  are  poisonous. 

EXERCISES 

Ex.  173.  Name  some  of  the  common  fats  found  in  plants  and 
animals.  What  is  produced  when  fat  is  heated  with  steam  under  pres- 
sure? Do  fats  always  consist  of  glycerin  united  with  one  or  more 
fatty  acids  ?  What  are  the  three  most  common  fatty  acids  ?  How  are 
the  fats  themselves  named  ?  Name  the  three  most  common  fats.  Do 
natural  fats  consist  of  one  of  these  fats  or  of  a  mixture  of  two  or  more  ? 

Ex.  174.  What  gives  the  characteristic  flavor  to  butter  fat  ?  Does 
this  substance  occur  in  any  other  natural  fat  ?  What  is  oleomargarine  ? 
How  is  the  flavor  of  butter  given  to  it?  What  is  renovated  butter? 

Ex.  176.  Write  out  the  formulas  for  olein  and  stearin.  How  many 
more  hydrogen  atoms  are  there  in  stearin  than  in  olein  ?  Can  hydro- 
gen be  added  to  olein  ?  What  is  this  process  called  ?  Name  a  product 
that  is  so  prepared.  Of  what  value  is  hydrogenation  in  soap  making? 

Ex.  176.  (Teacher)  Place  20  grams  of  lard  in  an  evaporating  dish 
or  a  granite-ware  cup  and  warm  to  melt  the  lard.  Dissolve  10  grams  of 
sodium  hydroxide  in  about  40  cc.  of  water.  Add  the  solution  slowly 
to  the  melted  fat.  Heat  gently,  with  constant  stirring,  until  a  few  drops 
of  the  mixture  dissolve  completely  in  clear  water  leaving  no  globules  of 
fat.  When  the  mixture  is  cool,  add  a  strong  solution  of  salt  and  the  soap 
will  separate  and  rise  to  the  top,  where  it  will  finally  solidify. 

Ex.  177.  Explain  the  changes  which  take  place  in  soap  making. 
Dissolve  some  of  the  soap  in  water  and  add  hydrochloric  acid.  The 
material  which  floats  on  the  top  consists  of  the  fatty  acids  which  were 


FATS,   OILS,  AND  SOAPS  269 

present  in  the  lard  and  the  soap.  To  another  portion  of  the  soap  solu- 
tion add  a  solution  of  calcium  chloride.  What  is  the  curd  in  this  case  ? 
Why  is  more  soap  necessary  with  hard  water  than  with  soft  water  ? 

Ex.  178.  (Teacher)  Half  fill  a  liter  distilling  flask  with  chopped 
green  leaves  of  peppermint,  spearmint,  wild  bergamot,  or  sweet  clover, 
and  add  200  cc.  of  water.  Connect  with  a  condenser  and  distill  until 
the  receiving  flask  contains  about  50  cc.  of  liquid.  A  few  drops  of  the 
essential  oil  will  be  found  floating  on  the  water. 


CHAPTER  XXXIII 
CARBOHYDRATES 

305.  THE  compounds  that  are  produced  most  abundantly 
by  growing  plants  are  substances  which  contain  carbon  com- 
bined with  hydrogen  and  oxygen,  the  latter  two  being  present 
in  the  proportion  in  which  they  are  found  in  water.  Because 
of  this  relation  between  the  hydrogen  and  oxygen  these  com- 
pounds are  collectively  known  as  carbohydrates.  Their 
importance  will  be  realized  when  it  is  said  that  this  group 
includes  the  sugars,  starches,  woods,  and  all  plant  fibers. 

,306.  Grape  sugar,  or  glucose,  as  its  name  signifies,  is  the 
sugar  found  naturally  in  grapes.  The  whitish  efflorescence 
on  raisins  and  dried  figs  is  glucose.  When  dry,  glucose  is  a 
waxy  mass  that  can  be  made  to  crystallize  only  with  great 
difficulty.  It  is  sweet  to  the  taste,  but  its  sweetening  power 
is  only  about  three  fifths  that  of  cane  sugar.  It  occurs  in 
many  fruits.  Commercially  glucose  appears  as  a  heavy 
sirup  and  in  this  case  is  produced  by  the  action  of  acids  on 
starch  (311).  It  is  the  principal  constituent  of  many  table 
sirups,  especially  those  labeled  corn  sirup.  It  is  also  used 
in  preserving  fruits  and  in  candy  making,  largely  because 
the  addition  of  about  10  per  cent  of  glucose  overcomes  the 
tendency  of  cane  sugar  to  crystallize. 

Glucose  is  a  good  food  and  there  is  no  reason  for  the  popular 
prejudice  against  it,  except  that  in  the  past  it  was  used  as  an 
adulterant  for  the  much  sweeter  cane  sugar. 

270 


CARBOHYDRATES  271 


The  formula  for  glucose  is  CeH^Oe-  When  acted  upon  by 
yeast  it  very  readily  ferments,  forming  ethyl  alcohol  and 
carbon  dioxide  (281).  Glucose  is  a  reducing  agent  (43)  and 
the  chemical  test  for  it  and  some  other  sugars  depends  on 
this  fact.  The  test  reagent  is  known  as  Fehling's  solution. 
It  is  made  by  mixing  solutions  of  copper  sulphate  and  sodium 
hydroxide  and  then  adding  Rochelle  salt  (292)  until  the 
precipitate  first  formed  is  redissolved.  This  liquid  may 
now  be  considered  as  a  solution  of  cupric  oxide  (CuO).  If  a 
reducing  agent  such  as  glucose  is  added  to  hot  Fehling's 
solution,  it  abstracts  oxygen  from  the  cupric  oxide,  leaving 
cuprous  oxide,  which  is  precipitated  : 

2  CuO  ->•  Cu2O  +  O. 

307.  Fruit  sugar,  or  fructose,  is  a  sugar  found  in  some 
fruits.  It  occurs  also  in  the  nectar  of  flowers  and,  therefore, 
is  a  constituent  of  honey,  in  which  it  is  associated  with  glu- 
cose. It  is  sweeter  than  glucose.  It  ferments  under  the 
action  of  yeast  but  not  so  readily  as  glucose. 

The  formula  for  fructose  is  CeH^Oe,  which  will  be  seen  to 
be  the  same  as  that  assigned  to  glucose.  It  often  happens 
in  organic  chemistry  that  two  or  more  entirely  distinct  com- 
pounds have  the  same  kind  and  number  of  atoms  in  the 
molecule.  The  explanation  offered  is  that  the  properties  of 
a  compound  depend  not  solely  upon  the  number  and  kind  of 
atoms  in  the  molecule,  but  upon  the  way  in  which  these  atoms 
are  arranged.  A  child  may  with  the  same  number  of  red, 
white,  and  blue  blocks  work  out  a  variety  of  patterns  by 
different  arrangements  of  the  blocks.  Likewise  the  same 
number  of  carbon,  hydrogen,  and  oxygen  atoms  may  be 
arranged  in  the  molecule  in  a  number  of  ways,  and  each 
different  arrangement  results  in  a  distinct  compound  with 


272 


ORGANIC   CHEMISTRY 


some  properties  peculiar  to  itself.  Two  or  more  compounds 
that  have  the  same  general  formula  are  known  as  isomeric 
compounds,  or  isomers. 

308.  Cane  Sugar.  As  ordinarily  used  the  term  sugar  refers 
to  cane  sugar,  or  sucrose,  which  has  the  formula  Ci2H22Oii. 
This  sugar  is  found  in  sugar  cane  (Fig.  138),  sorghum,  sugar 
beet,  and  the  sap  of  the  maple  tree,  as  well  as  in  many  fruits. 


FIG.  138.  — -  Growing  sugar  cane. 

There  is  more  of  this  sugar  in  nature  than  any  other  sugar. 
About  half  the  sugar  of  commerce  comes  from  sugar  beets, 
the  rest  largely  from  sugar  cane.  The  juice  of  the  cane,  or 
the  water  extract  of  the  beet,  is  first  treated  with  milk  of 
lime  (114)  to  neutralize  the  acids  and  to  precipitate  the 
albuminous  substances  that  are  present.  The  excess  of  lime 
is  removed  by  passing  carbon  dioxide  through  the  liquid, 
and  the  clarified  liquid  is  evaporated  in  vacuum  pans  until 
very  thick.  Upon  cooling,  the  sugar  separates  and  the  re- 


CARBOHYDRATES  .        273 

maining  liquid  is  removed  by  whirling  in  a  centrifugal 
machine.  The  product  is  a  brown  sugar  which  is  refined  by 
dissolving  it  in  water  and  filtering  the  solution  through  bone 
black  (91)  to  remove  the  coloring  matter,  and  again  concen- 
trating in  vacuum  pans.  This  treatment  produces  the  clear 
crystals  sold  under  the  name  of  granulated  sugar.  The  liquid 
left  after  the  separation  of  the  brown  sugar  is  called  molasses. 
The  annual  production  of  sugar  from  cane  and  sugar  beets 
amounts  to  over  ten  million  tons.  Whether  produced  from 
cane  or  beets  the  sugar  is  the  same  compound.  The  popular 
notion  that  cane  sugar  differs  from  beet  sugar  is  erroneous. 
Cane  sugar  when  pure  does  not  reduce  Fehling's  solution. 
If  the  sugar  is  boiled  with  dilute  acids  (sulphuric,  for  instance) 
and  the  acid  is  neutralized  with  an  alkali,  the  resulting  solu- 
tion has  a  strong  reducing  action.  This  is  due  to  the  fact  that 
the  molecule  of  cane  sugar  takes  on  water  and  is  changed  into 
a  molecule  each  of  glucose  and  fructose : 

Ci2H22On  +  H2O  ->-  C6Hi206  +  C6H12O6. 

cane  sugar  glucose  fructose 

The  acid  apparently  acts  as  a  catalytic  agent.  This 
change  of  cane  sugar  into  glucose  and  fructose  is  called  in- 
version, and  the  product  (the  mixture  of  glucose  and  fructose) 
is  known  as  invert  sugar.  In  jelly  making  the  acid  of  the 
fruit  always  inverts  a  part  of  the  sugar.  ^Vinegar  is  some- 
times added  in  candy  making  to  invert  part  of  the  sugar  so 
that  the  glucose  and  fructose  will  check  the  tendency  of  the 
cane  sugar  to  crystallize. 

Cane  sugar  does  not  ferment  readily.  After  a  time,  how- 
ever, it  does  undergo  alcoholic  fermentation,  for  the  yeast 
contains  a  substance  which  slowly  inverts  the  cane  sugar, 
and  the  resulting  glucose  and  fructose  readily  ferment. 

EV.  CHEM. 18 


274  ORGANIC  CHEMISTRY 

309.  Malt  sugar,  or  maltose,  is  a  sugar  having  the  same 
formula  as  cane  sugar  (isomer)  and  is  formed  by  the  action 
of  malt  on  starch  (311).     Malt,  which  is  made  by  steeping 
barley  in  water  until  it  germinates,  and  then  drying  it,  con- 
tains a  substance  called  diastase,  which  has  the  power  of 
changing    starch    into    maltose    (Ci2H22On).     Maltose  is  a 
reducing  sugar.     It  is  easily  fermented  and  is  the  inter- 
mediate product  in  the  formation  of  alcohol  from  starch. 
When  heated  with  dilute  acid  it  is  changed  into  glucose : 

CiaHaQu  +  H2O  ^  2  C6H12O6. 

maltose  glucose 

310.  Milk  sugar,   or  lactose,  is  another  isomer  of  cane 
sugar  that  is  found  only  in  milk.     It  is  produced  com- 
mercially from  the  whey  left  in  cheese  making.     It  is  much 
less  sweet  and  less  soluble  than  cane  sugar.     It  is  the  sugar 
most  commonly  used  in  medicine.     It  is  a  reducing  sugar  but 
does  not  readily  ferment.     Its  most  important  reaction  is  the 
change  into  lactic  acid  (290) : 

C12H22On  +  H20  -^  4  H.C3H503. 

lactose  lactic  acid 

311.  Starch  is  one  of  the  most  abundant  compounds  pro- 
duced by  plants.     It  forms  from  50  per  cent  to  75  per  cent 
of  the  dry  matter  of  seeds  and  tubers,  where  it  is  stored 
as  food  for  the  young  plant  before  it  is  able  to  obtain  its  own 
food.     In  this  country  most  of  the  starch  of  commerce  is 
prepared  from  corn,  while  in  Europe  potatoes  are  the  prin- 
cipal source. 

Starch  is  separated  from  corn  by  soaking,  grinding,  and 
washing  the  grain  in  water  and  then  filtering.  In  the  last 
process,  the  finely  divided  starch  passes  through  bolting 
cloth  and  then  is  allowed  to  settle  from  the  water  in  which  it 


CARBOHYDRATES 


275 


is  suspended.  Starch  occurs  in  the  plant  as  granules,  which 
vary  in  form  and  markings  according  to  the  plant  from  which 
they  are  derived  (Fig.  139).  It  is  possible  to  tell  the 
source  of  the  starch  by  examination  under  the  microscope. 

Starch  is  not  soluble  in  water.     When  treated  with  boiling 
water  the  granules  swell  and  burst,  forming  a  gelatinous 


FIG.  139.  —  Magnified  starch  granules.     1.  Potato.     2.  Wheat.     3.  Rice. 

mass  known  as  starch  paste.  It  is  colored  blue  by  iodine. 
It  has  the  composition  represented  by  the  formula  C6Hi0O5  ; 
but  there  are  good  reasons  for  believing  that  the  molecule  is 
really  much  larger  than  this  formula  suggests.  It  is  quite 
customary,  therefore,  to  write  the  formula  (C6HioO5)x,  in 
which  x  represents  an  unknown  number.  Starch  is  changed 
into  glucose  by  prolonged  boiling  with  dilute  acids  (306)  : 

H20  - 


Large  quantities  of  starch  are  used  for  the  production  of 
glucose,  which  is  prepared  commercially  by  boiling  corn 
starch  under  pressure  with  hydrochloric  acid.  The  acid  is 
then  neutralized  with  sodium  carbonate,  and  after  the  liquid 
has  been  clarified  with  bone  black  it  is  concentrated  to  a 
thick  sirup  containing  30  to  40  per  cent  of  glucose,  mixed 
with  dextrin  (312). 

Starch  is  a  valuable  constituent  of  many  foods.  It  is  used 
in  the  laundry,  for  the  making  of  library  or  photo  pastes,  in 


276  ORGANIC  CHEMISTRY 

the  finishing  of  cotton  cloth,  and  for  many  other  purposes. 
Sago  is  a  starch  prepared  from  certain  palm  trees.  Tapioca, 
a  starch,  comes  from  the  root  of  a  tropical  plant  called 
cassava. 

312.  Dextrin.     When  starch  is  heated  to  about  200°  C.  it 
is  changed  into  a  pale  yellow  powder  that  is  soluble  in  water 
and  is  not  colored  by  iodine.     This  substance  is  called  dextrin 
and  is  represented  by  the  same  general  formula  as  starch 
(CeHioOs),.     Its  solution  is  gummy,  and  dextrin  is  now  used 
as  a  substitute  for  the  natural  gums  in  making  mucilage. 
Dextrin  is  an  intermediate  product  in  the  formation  of  glu- 
cose from  starch;  consequently  commercial  glucose  usually 
contains  dextrin  as  well  as  glucose.     In  laundry  work  the 
heat  of  the  iron  converts  some  of  the  starch  into  dextrin, 
which  gives  a  glossy  finish  to  the  cloth. 

313.  Cellulose  is  the  substance  that  forms  the  basis  of  the 
woody  fiber  of  plants.     It  is  found  most  abundantly  in  the 
stems,  roots,  and  leaves  of  plants,  particularly  at  maturity. 
It  is  the  structural  basis  of  the  vegetable  world  and  forms  the 
framework  of  every  plant  cell.     In  some  plants  it  is  the  most 
abundant  material  present ;  in  hay  and  coarse  fodder  •  it 
makes  up  30  to  40  per  cent  of  the  dry  matter.     Cotton  and 
linen  are  examples  of  almost  pure  cellulose.     When  quite 
pure,  cellulose  is  a  colorless  material  insoluble  in  water  and 
differing  in  texture  according  to  its  source.     It  is  assigned  the 
same  general  formula  as  starch  (C6Hi0O5)a.     In  the  case  of 
cellulose,  however,  x  probably  stands  for  a  larger  multiple 
than  it  does  in  the  formula  for  starch.      It  is  evident  that 
cellulose  plays  an  important  role  in  providing  material  for 
fuel,  shelter,  and  raiment  for  mankind.     It  is  used  in  paper 
making  and  in  the  preparation  of  guncotton,  celluloid,  and 
many  other  useful  materials. 


CARBOHYDRATES  277 

314.  Nitrogen    Compounds    of    Cellulose.    Nitric    acid 
unites  with  cellulose  in  several  proportions,  and  the  resulting 
compounds  are  known  collectively  as  nitrocellulose,  or  gun- 
cotton.     This  substance,  which  is  highly  explosive,  is  the  basis 
of  smokeless  powder,  which  has  supplanted  black  gunpowder 
in  military  operations.    Some  of  the  nitrocellulose  compounds 
dissolve  in  a  mixture  of  alcohol  and  ether,  forming  the  sub- 
stance known  as  collodion.   Collodion  is  used  as  liquid  court- 
plaster  and  in  the  making  of  photographic  films,  because  on 
the  evaporation  of  the  ether  and  alcohol  a  tough,  trans- 
parent film  remains.     Celluloid  is  made  by  combining  gun- 
cotton  with  gum  camphor.     It  is,  therefore,  very  inflam- 
mable, and  many  serious  accidents  have  occurred  from  care- 
lessly allowing  celluloid  to  come  into  contact  with  a  flame. 
A  mixture  of  guncotton  and  nitroglycerin  is  used  under  the 
name  of  blasting  gelatin,  especially  for  heavy  blasting,  as  it  is 
a  very  powerful  explosive. 

315.  Gums  and  Pectin  Bodies.     Closely  related  to  the 
sugars  are  the  gums,  such  as  gum  arabic  and  those  that 
exude  from  peach  and  cherry  trees.     Gum  arabic  is  an  isomer 
of  cane  sugar  (C^H^On).     It  is  used  in  making  mucilage  and 
in  the  better  grades  of  gumdrops.     Pectin  bodies  are  found 
in  many  fruits  and  some  vegetables.     They  are  jelly  like  sub- 
stances that  are  soluble  in  hot  water  and  are  commonly 
known  as  fruit  jellies.     Gums  and  the  pectin  bodies  are  con- 
sidered to  have  the  same  food  value  as  starch  and  sugar. 

EXERCISES 

Ex.  179.  What  is  meant  by  the  term  carbohydrate  ?  Are  the  car- 
bohydrates of  much  importance?  What  is  the  formula  for  glucose? 
Where  is  it  found  in  nature  ?  How  is  commercial  glucose  manufactured  ? 
For  what  is  it  used  ? 


278  ORGANIC  CHEMISTRY 

Ex.  180.  Heat  a  little  Fehling's  solution  to  boiling  and  add  a  few 
drops  of  a  solution  of  pure  glucose,  or  of  Karo  sirup.  Heat  again. 
The  red  precipitate  of  cuprous  oxide  is  the  test  for  glucose  or  other 
reducing  sugar.  Explain  the  action  of  glucose  on  Fehling's  solution. 
Soak  a  few  raisins  in  water  and  test  the  solution  for  grape  sugar. 

Ex.  181.  What  is  the  formula  for  fructose  ?  Compare  with  that  for 
glucose.  How  do  you  explain  the  fact  that  there  are  two  compounds 
with  the  same  formula  ?  What  is  an  isomer  ?  What  sugars  are  found 
in  honey  ?  Test  a  sample  of  honey  with  Fehling's  solution. 

Ex.  182.  What  sugar  is  found  most  abundantly  in  nature?  Name 
some  of  the  plants  that  contain  it.  From  what  plants  is  it  prepared 
on  a  commercial  scale?  How  is  the  brown  sugar  changed  to  white 
sugar  ?  What  is  molasses  ?  Is  there  any  difference  between  sugar  from 
cane  and  from  beets  ?  What  is  the  formula  for  cane  sugar  ? 

Ex.  183.  Test  a  solution  of  granulated  sugar  with  Fehling's  solu- 
tion. To  a  little  of  the  solution  add  a  few  drops  of  hydrochloric  acid  and 
boil  two  minutes.  Add  a  pinch  of  sodium  carbonate  to  neutralize  the 
acid  and  test  with  Fehling's  solution.  What  change  has  taken  place  in 
the  sugar  ? 

Ex.  184.  Test  a  sample  of  jelly  from  home  for  glucose.  Fruit 
juice  and  cane  sugar  were  used  in  making  the  jelly  —  account  for  the 
presence  of  glucose.  Why  is  vinegar  or  cream  of  tartar  sometimes  used 
in  homemade  candies  ? 

Ex.  185.  What  is  the  formula  for  maltose  ?  How  is  it  prepared  ? 
What  is  the  formula  for  milk  sugar?  Compare  this  with  the  formula 
for  cane  sugar.  Are  they  isomers  ?  What  is  the  sole  source  of  milk 
sugar  ?  What  product  is  formed  from  milk  sugar  when  milk  sours  ? 

Ex.  186.  Reduce  two  large  potatoes  to  a  pulp  with  a  vegetable 
grater.  Tie  the  pulp  in  a  clean  thin  cloth  and  squeeze  it  into  a  vessel  of 
water,  occasionally  dipping  the  bag  into  the  water.  Pour  the  liquid 
into  a  tall  cylinder  and  allow  the  starch  to  settle.  Pour  off  the  clear 
water,  and  transfer  the  starch  to  a  shallow  dish  and  allow  it  to  dry. 

Ex.  187.  What  can  you  say  about  the  importance  of  starch? 
From  what  is  the  starch  of  commerce  produced?  Is  starch  soluble 
in  water  ?  What  happens  to  it  when  boiled  with  water  ?  What  is  the 
formula  ?  Why  is  the  formula  multiplied  by  x  ?  Give  some  important 
uses  for  starch. 


CARBOHYDRATES  279 

Ex.  188.  Put  a  little  of  the  starch  from  Ex.  186  into  a  test  tube  and 
boil  it  with  water.  Add  a  drop  of  a  solution  of  iodine  and  potassium 
iodide.  What  change  takes  place  ?  This  is  the  test  for  starch.  Test 
for  the  presence  of  starch  in  various  seeds  and  vegetables. 

Ex.  189.  Boil  a  little  starch  in  water  and  test  part  of  the  liquid  with 
Fehling's  solution.  What  is  the  result  ?  To  another  part  of  the  boiled 
starch  add  a  few  drops  of  hydrochloric  acid  and  boil  three  or  four  minutes. 
Test  with  Fehling's  solution.  What  difference  do  you  note?  What 
change  has  taken  place  in  the  starch  ?  How  is  commercial  glucose  sirup 
prepared  ? 

Ex.  190.  How  is  dextrin  prepared?  What  is  the  formula?  Is  it 
soluble  in  water  ?  Is  it  colored  by  iodine  ?  For  what  is  it  used  ?  Why 
does  the  crust  of  bread  have  a  sweeter  taste  than  the  crumb  ? 

Ex.  191.  (Teacher)  If  a  compound  microscope  is  at  hand  prepare 
slides  of  starch  from  potatoes,  corn,  and  other  food  products.  Have  the 
class  observe  and  make  drawings  of  the  different  starch  grains. 

Ex.  192.  What  is  cellulose  ?  In  what  parts  of  the  plant  is  it  most 
abundant?  Is  it  an  important  substance?  Give  two  examples  of  al- 
most pure  cellulose.  What  is  its  formula?  What  explosive  materials 
are  prepared  from  cellulose  ?  What  is  collodion  ?  Celluloid  ? 

Ex.  193.  What  are  the  substances  known  as  gums?  Give  the 
formula  of  gum  arabic.  Compare  this  with  the  formula  for  cane  sugar. 
For  what  is  it  used  ?  What  are  the  pectins  and  where  are  they  found  ? 
Of  what  importance  is  pectin  in  jelly  making  ? 


CHAPTER  XXXIV 
ORGANIC   NITROGEN   COMPOUNDS 

316.  THE  organic  compounds  so  far  studied,  with  the  ex- 
ception of  nitroglycerin  and  nitrocellulose,  contain  not  to 
exceed  three  elements;      namely,   carbon,   hydrogen,   and 
oxygen.     If  a  piece  of  lean  meat  or  a  bit  of  dried  egg  white  is 
placed  in  a  deep  test  tube  and  heated,  the  odor  of  ammonia 
can  be  detected  in  the  escaping  gases.     A  piece  of  moistened 
red  litmus  paper  held  in  these  gases  will  be  changed  to  blue. 
This  formation  of  ammonia  from  the  meat  or  egg  will  take 
place  more  rapidly  if  the  material   is  first  mixed  with  soda- 
lime.     Evidently,  then,  these  substances  contain  nitrogen, 
or  the  ammonia  could  not  have  been  formed.     During  the 
heating,  water  vapor  is  given  off,  and  charcoal  remains  in 
the  tube ;  the  meat  and  ^gg,  therefore,  must  contain  carbon, 
hydrogen,  and  oxygen  as  well  as  nitrogen.     If  a  piece  of  paper 
moistened  with  sugar  of  lead  is  held  in  the  escaping  gases  in 
the  above  experiment,  it  will  be  blackened,  showing  the  pres- 
ence of  hydrogen  sulphide,  which  indicates  that  sulphur  also 
is  found  in  the  egg  and  meat.     Both  meat  and  egg  belong 
to  a  large  class  of  compounds  known  as  proteins. 

317.  Proteins  are  generally  distributed  in  the  animal  and 
vegetable  kingdoms.     They  are  not  nearly  so  abundant  as 
the  carbohydrates.     It  is  estimated  that  ten  times  as  much 
carbohydrate  as  protein  is  produced  in  the  vegetable  kingdom. 
All  proteins  contain  the  four  elements,  carbon,  oxygen,  hy- 
drogen, and  nitrogen,  and  most  of  them  contain  sulphur  as 
well.     Some  of  the  proteins  contain  in  addition  to  the  five 

280 


ORGANIC  NITROGEN   COMPOUNDS  281 

elements  mentioned,  a  small  amount  of  phosphorus.  No  one 
has  been  able  to  determine  the  formula  for  any  of  the  proteins, 
and  they  are  thought  to  be  the  most  complex  of  all  the  chemi- 
cal compounds.  The  complexity  of  the  molecule  may  be 
inferred  from  the  fact  that  the  most  careful  experimenters 
estimate  the  molecular  weight  anywhere  from  16,000  to 
50,000.  When  this  molecular  weight  is  compared  with  that 
for  sugar  (C^H^On),  which  is  342,  some  idea  may  be  formed 
of  what  an  enormous  number  of  atoms  the  protein  molecule 
must  contain.  Most  of  the  proteins  found  in  nature  are  in- 
soluble in  water,  although  there  are  a  number  of  soluble  pro- 
teins, the  white  of  egg,  for  example.  Some  which  will  not 
dissolve  in  water  are  soluble  in  weak  salt  solutions.  The 
proteins  unite  with  dilute  acids  and  alkalies,  forming  com- 
pounds that  are  sometimes  soluble  in  water  and  sometimes 
insoluble.  Concentrated  acids  and  alkalies  dissolve  all  the 
proteins.  The  proteins  decay  very  readily,  and  their  de- 
composition is  accompanied  by  offensive  odors,  as  for  ex- 
ample that  of  rotten  eggs. 

318.  Tests  for  Proteins.  While  there  are  a  great  many 
kinds  and  classes  of  proteins,  there  are  a  few  tests  that  apply 
to  all  proteins,  which  may  be  used  to  show  the  presence  of 
protein  in  any  substance  that  is  being  examined  : 

(1)  Nitric  acid  gives  a  permanent  yellow  color  with  pro- 
teins upon  warming.     The  yellow  color  produced  when  nitric 
acid  is  dropped  on  the  hands  is  due  to*  the  reaction  of  the 
nitric  acid  with  the  protein  of  the  skin.     If  ammonia  water 
is  added  to  the  protein  which  was  turned  yellow  by  nitric 
acid,  it  will  be  changed  to  an  orange  color. 

(2)  A  solution  of  mercury  in  nitric  acid  (mercuric  nitrate), 
known  as  Millon's  reagent,  gives  a  brick  red  color  with  pro- 
teins when  heated. 


282 


ORGANIC  CHEMISTRY 


(3)  Tannic  acid  forms  a  tough,  leathery  compound  with 
proteins.  If  the  protein  is  in  solution,  tannic  acid  throws  it 
down  in  the  form  of  a  leathery  precipitate.  The  change  of 
animal  hides  into  leather  is  largely  due  to  the  formation 
of  tough,  insoluble  compounds  by  the  action  of  the  tannin 
on  the  proteins  of  the  skin  or  hide. 

319.  Proteins  Insoluble  in  Water.  The  muscle,  or  lean 
meat,  of  all  animals  consists  largely  of  insoluble  protein, 
although  there  is  a  small  amount  of  soluble  protein  present, 
as  will  be  seen  later.  Another  important  source  of  insoluble 
proteins  is  the  wheat  kernel.  If  a  cupful  of  wheat  flour  is 
made  into  dough  with  a  small  quantity  of  water  and  then 

wrapped  in  a  thin  cloth 
and  kneaded  under 
water  (Fig.  140),  the 
starch  of  the  flour  will 
pass  through  the  cloth, 
leaving  a  sticky,  elastic 
mass  (Fig.  141),  which 
is  the  protein  material 
known  as  the  gluten  of 
the  wheat.  Gluten  con- 
sists of  two  proteins; 

one>   9^dm,    IS    a    glue- 

like  body  that  binds  to- 

gether the  particles  of  flour  in  the  dough  ;  the  other,  glu- 
tenin,  is  a  fine,  gray  material  that  does  not  have  the  bind- 
ing property  of  the  gliadin.  It  is  the  gliadin  in  wheat  that 
makes  possible  a  light  loaf  of  bread.  All  the  grains  contain 
proteins  similar  to  the  gluten  of  wheat,  although  rye  is 
the  only  other  grain  in  which  the  gluten  is  of  the  quality 
to  make  a  good  dough. 


FIG.  140.—  The  separation  of  gluten  from  wheat. 


ORGANIC  NITROGEN  COMPOUNDS  283 

Casein,  the  important  protein  of  milk,  seems  to  be  dis- 
solved but  is  really  held  in  mechanical  suspension.  Its  im- 
portant characteristic 
is  its  behavior  toward 
acids  and  rennet.  When 
either  an  acid  or  rennet 
is  added  to  milk,  the 
casein  separates  in  a 
thick  curd.  Rennet  ex- 
tract is  made  by  soak- 
ing the  linings  of  the 

i  P  FIG.  141.  —  Showing  the  elasticity  of  gluten. 

stomachs     of    young 

calves  in  a  solution  of  common  salt.  The  young  stomach  con- 
tains a  substance  called  rennin  which  has  the  property  of  co- 
agulating casein.  When  milk  sours  naturally,  the  lactic  acid 
unites  with  the  casein  and  forms  a  curd.  The  curds  formed 
by  acids  and  that  by  rennet  are  both  used  in  cheese  making. 

320.  Albumins  are  proteins  that  are  soluble  in  water.     The 
most  familiar  example  is  the  white  of  egg.     Albumins  coagu- 
late when  heated,  as  is  well  shown  when  an  egg  is  boiled  or 
fried  until  the  white  becomes  hard.     If  a  solution  of  egg  white 
is  boiled,  the  albumin  coagulates  and  is  precipitated.     Al- 
bumin occurs  to  a  limited  extent  in  meat,  as  can  be  shown  by 
rubbing  chopped  raw  meat  in  a  mortar  with  water,  filtering 
it,  and  then  heating  the  filtrate.     When  meat  is  boiled  a  scum 
of  albumin  is  often  found  on  the  surface  of  the  water,  espe- 
cially if  the  meat  was  placed  in  cold  water  in  the  beginning. 
Albumin  is  present  in  milk  and  is  left  in  solution  in  the  whey 
when  casein  is  coagulated  either  by  acid  or  rennet.     Albumin 
is  also  one  of  the  constituents  of  the  blood. 

321.  Peptones  are  proteins  that  are  soluble  in  water  and 
are  not  coagulated  by  heat.     They  are  usually  formed  by  the 


284  ORGANIC  CHEMISTRY 

actions  of  ferments  on  the  other  proteins.  When  gastric 
juice,  for  instance,  acts  on  meat  or  coagulated  albumin,  the 
protein  disappears,  forming  a  more  or  less  clear  solution. 
Since  this  solution  gives  no  precipitate  when  heated,  it  does 
not  contain  albumin ;  but  by  applying  the  tests  'described 
above  (318)  it  can  be  shown  that  protein  is  present.  Pep- 
sin, a  substance  prepared  from  the  stomach  of  the  pig,  can 
be  used  to  perform  this  experiment  in  the  laboratory.  Some 
of  the  so-called  predigested  or  peptonized  foods  contain  pep- 
tones prepared  by  the  artificial  digestion  of  the  food  by  means 
of  pepsin.  The  proteins  of  the  food  must  be  converted  into 
peptones  in  the  stomach  and  intestines  before  they  can  be 
absorbed  and  pass  into  the  blood.  Peptones  are  not  present 
in  ordinary  foods  in  appreciable  amounts  but  are  formed  from 
the  foods  during  digestion. 

322.  Importance  of  Proteins.     Proteins  are  present  in  all 
plant  and  animal  cells.     The  vital  part  of  the  cell,  the  proto- 
plasm, consists  of  protein  material,  and  consequently  it  will 
be  seen  that  all  life  depends  on  the  proteins.     The  muscles  of 
animals  consist  largely  of  proteins ;  and  the  only  way  in 
which  the  muscles  can  be  built  up  and  repaired  is  by  means 
of  the  proteins  of  the  food,  since  the  animal  body  is  not  able  to 
manufacture  proteins  from  other  materials.     The  proteins, 
then,  have  a  place  that  cannot  be  filled  by  the  carbohydrates, 
fats,  or  any  other  compounds.     All  parts  of  the  plant  con- 
tain some  protein ;    but  the  seeds  contain  the  most,  since  it 
is  stored  there  for  the  use  of  the  plantlet  when  it  begins 
its    growth.     It    will    be    seen   later   that   the    plant    can 
manufacture   these    complex    proteins    from    very   simple 
substances. 

323.  Gelatin  and  Other  Albuminoids.    There  is  another 
class  of  nitrogen  compounds,  somewhat  resembling  the  pro- 


ORGANIC  NITROGEN   COMPOUNDS  285 

teins,  to  which  the  name  albuminoids  has  been  given.  The 
best-known  example  of  this  class  is  gelatin,  which  is  obtained 
from  the  connective  tissue  and  bones  of  animals.  Commer- 
cial glue  is  an  impure  gelatin.  Gelatin  dissolves  in  hot  water 
and  forms  a  jellylike  mass  upon  cooling.  While  it  is  a  good 
food  product  and  is  easily  digested,  it  will  not  take  the  place 
of  protein  in  the  food.  Keratin  is  a  hard,  horny  albuminoid 
found  in  the  horns,  hoofs,  hair,  nails,  and  feathers.  Mucin, 
the  chief  constituent  of  mucus,  gives  the  sliminess  to  the 
secretion  of  the  mucous  membrane.  It  is  present  in  the 
saliva. 

324.  Amines.     There  is  a  marked  difference  between  the 
simple  nitrogen  compounds  that  the  plants  take  in  from  the 
soil  (nitrates  and  ammonia)  and  the  very  complex  proteins 
that  they  store  in  their  seeds.     It  is  not  surprising,  therefore, 
to  find  that  there  are  intermediate  compounds,  or,  in  other 
words,  that  the  building  up  of  a  protein  is  not  a  matter  of 
one  change  but  takes  place  by  steps.     Some  of  the  inter- 
mediate compounds  are  known  and  have  been  assigned  the 
name  of  amines.     Their  chief  interest  for  the  purpose  of  this 
text  lies  in  the  fact  that  they  are  intermediate  compounds  in 
the  building  up  of  proteins,  and  that  when  the  protein  is 
broken  down  during  digestion  or  decay,  the  amines  are  pro- 
duced before  the  nitrogen  is  finally  changed  back  to  ammonia 
or  nitric  acid  (168). 

325.  Protein   Production   and   Destruction.     The   plant 
produces  protein  by  a  series  of  changes  about  as  follows  : 

(1)  Ammonia  or  nitrate  is  taken  from  the  soil. 

(2)  An  amine  is  formed  from  ammonia. 

(3)  A  protein  is  finally  formed  from  the  amine. 

When  animals  consume  the  plant  as  food  the  reverse 
order  of  changes  takes  place : 


286  ORGANIC  CHEMISTRY 

(1)  The  protein  is  digested  and  made  over  into  animal 
protein. 

(2)  The  animal  protein  is  finally  broken  down  into  amines. 

(3)  The  amine  is  expelled  from  the  body  as  waste  matter. 

(4)  In  the  soil  the  amine  is  changed  into  ammonia  and 
nitric  acid  by  the  bacteria  and  is  ready  to  begin  again  this 
cycle  of  changes. 

326.  Alkaloids  are  nitrogenous  organic  compounds  found 
in  many  animals  and  plants,  but  not  to  any  appreciable 
amount  in  true  food  plants.  They  somewhat  resemble  am- 
monia in  their  chemical  behavior  and  are,  therefore,  called 
alkaloids  (like  alkalies).  They  form  the  so-called  active 
principle  of  many  of  the  plants  used  in  medicine.  The 
following  are  some  of  the  principal  alkaloids  : 

Caffeine  (C8HioN4C^),  from  coffee  and  tea. 
Quinine  (€201124X202),  from  Peruvian  bark. 
Strychnine  (CaiHa^Qg),  from  nux  vomica  bean. 
Morphine  (Ci7Hi9XO3),  from  the  poppy. 
Nicotine  (Ci0Hi4N2),  from  tobacco. 

Alkaloids  are  also  formed  at  times  in  the  animal  body.  Some 
of  the  alkaloids  formed  during  the  decomposition  of  proteins 
are  extremely  poisonous  and  are  known  as  ptomaines.  They 
sometimes  occur  in  stale  meat,  fish,  and  cheese. 

EXERCISES 

Ex.  194.  Place  a  piece  of  lean  meat  in  a  test  tube  fitted  with  a 
cork  in  which  is  a  small  glass  tube.  Heat  over  the  flame.  Note  the 
odor  of  the  escaping  gas.  Hold  a  piece  of  moist  red  litmus  paper  in  the 
gas.  Test  with  sugar  of  lead  paper.  Repeat  the  experiment  with  some 
peas  or  beans.  Mix  a  quarter  of  a  test  tube  full  of  dry  clover  with  an 
equal  bulk  of  soda-lime  and  heat  and  test  as  above.  Have  you  any  evi- 


ORGANIC  NITROGEN  COMPOUNDS  287 

dence  that  ammonia  was  formed?  Was  sulphur  present  in  the  gas? 
What  was  the  source  of  these  substances  ? 

Ex.  196.  What  can  you  say  about  the  distribution  of  proteins  in 
nature  ?  Are  they  as  abundant  as  the  carbohydrates  ?  What  chemical 
elements  are  found  in  the  proteins  ?  Is  the  protein  molecule  very  com- 
plex ?  What  effect  do  acids  and  alkalies  have  on  proteins  ? 

Ex.  196.  To  a  little  egg  white  add  a  few  drops  of  Millon's  reagent 
and  warm  the  mixture.  What  is  the  result  ?  Try  the  same  experi- 
ment with  crushed  wheat  or  corn,  milk,  or  other  foodstuffs.  Which 
gave  the  test  for  proteins  ? 

Ex.  197.  (Teacher)  Mix  a  cupful  of  flour  to  a  dough  with  water. 
Place  it  in  a  cloth  bag  and  knead  it  under  water  (Fig.  140)  until  all  the 
starch  has  been  washed  out.  Examine  the  material  left  in  the  cloth. 
Is  it  sticky  and  elastic  ?  What  is  this  substance  ?  Make  the  test  with 
Millon's  reagent  on  a  small  piece  of  it.  What  other  substances  can  you 
name  that  belong  to  the  group  of  insoluble  proteins  ? 

Ex.  198.  Dissolve  the  white  of  a  raw  egg  in  about  a  pint  of  water 
and  use  it  for  the  following  tests  :  (1)  Heat  a  part  of  the  solution  to 
boiling  in  a  test  tube.  What  happens?  (2)  To  another  portion  of 
the  egg-white  solution  add  tannic  acid.  What  is  the  result  ?  ^ 

Ex.  199.  Place  10  grams  of  ground  oats  in  a  bottle  with  50  cc. 
of  water.  Cork  and  shake  the  bottle  vigorously  and  let  it  stand  for 
half  an  hour  or  until  the  next  period.  Filter  and  test  the  filtrate  with 
tannic  acid.  Is  there  any  albumin  in  the  oats  ?  Mention  some  other 
materials  which  contain  albumin. 

Ex.  200.  (Teacher)  Dissolve  five  grams  of  commercial  scale 
pepsin  in  a  quart  of  water  containing  5  drops  of  hydrochloric  acid. 
Pass  the  white  of  a  hard-boiled  egg  through  a  sieve  and  place  it  in  a  flask 
with  250  cc.  of  the  above  pepsin  solution.  Place  the  flask  in  a  water 
bath  and  keep  at  blood  temperature  for  four  or  five  hours.  What  action 
did  the  pepsin  have  on  the  congested  egg  albumin  ?  Filter  some  of  the 
solution  for  use  in  the  next  exercise. 

Ex.  201.  Heat  a  portion  of  the  solution  from  the  last  exercise  to 
ascertain  whether  it  contains  albumin.  To  another  portion  add  tannic 
acid.  To  another  add  Millon's  reagent  and  heat  it.  Does  the  solu- 
tion contain  albumin  ?  Does  it  contain  some  kind  of  protein  ?  What 
are  these  soluble  proteins  called  ?  Are  peptones  present  in  large  quan- 
tities in  foods  ?  Are  they  produced  during  digestion  ? 


288  ORGANIC  CHEMISTRY 

Ex.  202.  Why  are  proteins  vital  to  plant  and  animal  life  ?  Where 
does  the  animal  get  the  material  to  build  its  muscle  ?  Can  the  animal 
manufacture  proteins  ?  In  what  part  of  the  plant  is  the  most  protein 
found  ?  Why  is  the  protein  stored  in  the  seed  ?  Can  the  plants  manu- 
facture protein  ? 

Ex.  203.  (Teacher)  Obtain  a  package  of  any  of  the  culinary 
gelatins  and  prepare  a  jelly  with  the  amount  of  water  recommended  in 
the  printed  directions.  To  what  class  of  compounds  does  gelatin 
belong  ?  What  is  the  source  of  gelatin  ?  What  is  the  difference  between 
gelatin  and  glue?  Name  an  albuminoid  found  in  bones  and  hair; 
one  found  in  mucus. 

Ex.  204.  Does  the  plant  form  intermediate  compounds  between  the 
nitrates  and  the  proteins  ?  What  are  some  of  the  compounds  called  ? 
Outline  the  cycle  of  changes  in  the  production  and  destruction  of  pro- 
teins. What  are  the  alkaloids  ?  Name  some  of  the  common  alkaloids^ 
What  is  meant  by  a  ptomaine  ? 


CHAPTER  XXXV 
COMPOSITION   OF  PLANTS 

327.  Water.  All  plants  and,  indeed,  all  food  materials 
contain  water  which  in  many  cases  makes  up  the  larger 
portion  of  their  weight.  Green  plants,  such  as  the  mature 
corn  plant,  contain  as  much  as  80  per  cent  of  water,  while 
some  of  the  more  succulent  plants  like  cabbages,  lettuce, 
and  spinach  may  contain  as  high  as  90  per  cent  of  water. 
In  general  it  may  be  said  that  the  younger  the  plant  the 
larger  the  percentage  of  water  it  contains,  and  that  as  the 
plant  matures  the  percentage  of  water  is  decreased.  The 
stems  or  woody  parts  of  plants  contain  less  water  than 
the  leaves.  The  juicy  fruits,  such  as  oranges,  and  straw- 
berries, often  contain  over  90  per  cent  of  water,  while  the 
grains  may  be  as  low  as  10-15  per  cent  in  moisture  con- 
tent. Many  of  the  plants  and  plant  products  are  partially 
dried  to  remove  the  water  before  being  used  as  foods  for 
man  or  domestic  animals,  but  even  well-cured  hay,  or  such 
a  dry  substance  as  wheat  flour,  still  contains  about  10  per 
cent  of  water. 

The  amount  of  moisture  in  a  substance  is  determined  in 
the  laboratory  by  heating  the  material  for  several  hours  at 
the  temperature  of  boiling  water.  By  this  means  the  water 
in  the  plant  or  other  substance  is  converted  into  steam  and 
thus  expelled.  The  material  is  usually  dried  in  a  water  oven 
EV.  CHEM.  — 19  289 


290 


ORGANIC  CHEMISTRY 


similar  to  the  one  shown  in  Fig.  142.  The  walls  of  this  oven 
are  double,  the  space  between  them  being  partially  filled  with 
water  which  is  kept  boiling  by  means  of  a  gas  burner  placed 

beneath  the  oven.  In  such  an  oven 
the  substance  being  dried  may  be 
kept  heated  without  danger  of  the 
temperature  rising  above  100°  C. 
and  scorching  the  material.  Ovens 
heated  by  electricity  are  also  used, 
the  heat  being  adjusted  by  a  reg- 
ulator which  prevents  too  great  a 
rise  in  temperature. 

328.  Dry  Matter.  The  dry  mat- 
ter of  a  material  is  the  portion  left 
after  all  the  water  has  been  re- 
moved. The  dry  matter  in  plant 
products  varies  within  wide  limits, 
being  as  low  as  5-6  per  cent  in  some  fruits  and  over  90  per 
cent  in  certain  cereal  products.  The  amount  and  composi- 
tion of  the  dry  matter  in  a  food  material  determines  its  value 
as  a  nutrient. 

329.  Plant  Ash.  The  ash  of  a  plant  or  of  any  substance  is 
that  portion  that  remains  after  the  substance  is  burned  at 
the  lowest  temperature  necessary  for  complete  combustion. 
It  corresponds  in  a  general  way  to  the  ashes  left  in  the  stove 
when  wood  is  burned.  The  ash  of  the  plant  is  sometimes 
spoken  of  as  the  mineral  matter,  or  as  the  inorganic  matter  of 
the  plant,  and  also  as  the  non- volatile  part.  It  includes  all 
of  the  material  which  the  plant  obtained  from  the  soil  with 
the  exception  of  the  water  and  nitrogen,  and  possibly  part  of 
the  sulphur  and  phosphorus,  which  disappear  when  the 
plant  is  burned. 


FIG.  142.  —  Water  oven  for  the 
determination  of  moisture  in  plant 
and  animal  products. 


COMPOSITION  OF  PLANTS  291 

The  percentage  of  ash  is  determined  in  the  laboratory  by 
igniting  a  small  quantity  of  the  material  (two  grams)  in  a 
platinum  or  porcelain  dish  (Fig.  17)  until  all  the  carbon  is 
burned  and  a  white  or  nearly  white  ash  remains.  During 
the  experiment  the  material  must  be  carefully  protected 
from  currents  of  air,  which  might  blow  away  the  light 
particles  of  the  ash.  The  weight  of  the  ash  obtained  in 
this  way  divided  by  the  weight  of  the  material  taken  for 
the  experiment  gives  the  percentage  of  ash  in  the  substance. 

330.  Composition  and  Amount  of  Ash  in  Plants.  The  ash 
of  all  plants  contains  measurable  quantities  of  nine  chemical 
elements  — potassium,  calcium,  sodium,  iron,  magnesium, 
phosphorus,  sulphur,  chlorine,  and  silicon.  Traces  of  alu- 
minum and  manganese  also  are  found  in  the  ash.  None  of 
the  elements  of  the  ash  existed  in  the  plant  in  the  elemen- 
tary or  free  state ;  but  they  are  always  in  chemical  combina- 
tion forming  salts,  or  are  combined  with  the  elements  that 
form  the  organic  part  of  the  plant.  It  has  been  shown,  for 
example,  that  potassium  occurs  in  grapes  as  acid  potassium 
tartrate  (292)  and  that  phosphorus  and  sulphur  are  con- 
tained in  certain  of  the  proteins  (317). 

Some  plants  contain  much  more  ash  than  others,  and  there 
is  great  variation  in  the  percentage  composition  of  the  ash 
of  different  plants.  The  ash  of  clover  hay  contains  nearly 
four  times  as  much  calcium  as  the  ash  of^  timothy  hay,  but 
only  one  fifth  as  much  silicon.  The  ash  is  not  evenly  dis- 
tributed throughout  all  parts  of  the  plant.  In  corn  the 
amount  of  ash  in  the  different  parts  of  the  plant  is  as  follows  : 

Roots 5.8  per  cent 

Leaves  . 8.1  per  cent 

Stems 6.6  per  cent 

Grain 1.4  per  cent 


292  ORGANIC  CHEMISTRY 

331.  Organic  Matter.     That  part  of  the  plant  which  com- 
pletely burns  and  passes  off  in  the  form  of  gaseous  products 
is  termed  organic  matter.     It  is  determined  in  the  laboratory 
by  subtracting  the  percentage  of  ash  from  the  dry  matter. 
The  organic  matter  includes  the  proteins,  carbohydrates, 
fats,  organic  acids,  and  other  so-called  organic  compounds  of 
the  plant.     It  is  customary  to  divide  the  organic  constituents 
of  the  plant  into  two  large  classes ;  namely,  (1)  nitrogenous, 
and  (2)  non-nitrogenous,  the  division  depending  upon  the 
presence  or  absence  of  the  element  nitrogen  in  the  compounds. 

332.  Nitrogenous  Compounds.     The  proteins  are  the  most 
important  of  the  nitrogenous  constituents  of  plants.     Most 
of  the  proteins  found  in  plants  belong  to  the  insoluble  class, 
although  the  albumins  are  found  to  a  limited  extent.     There 
are  doubtless  a  great  number  of  different  plant  proteins, 
but  only  a  few  of  them  have  been  isolated  in  the  pure  state 
and  carefully  studied.     The  proteins  are  found  in  all  parts 
of  the  plant,  but  are  much  more  abundant  in  the  seeds. 
The  leaves  contain  more  protein  than  do  the  stems  or  roots. 

All  parts  of  a  plant  are  composed  of  minute  cells,  lying 
close  together.  These  cells  are  so  small  that  the  compound 
microscope  must  be  used  in  order  to  see  them.  The  cells 
contain  a  clear,  granular  substance,  called  protoplasm,  which 
has  about  the  consistency  of  the  white  of  egg.  It  is  the 
living  substance  of  the  cell,  and  the  growth  and  functions  of 
the  plant  depend  upon  the  activity  of  the  protoplasm.  It 
is  not  known  exactly  what  protoplasm  is,  but  it  is  un- 
doubtedly largely  composed  of  proteins. 

To  find  the  amount  of  protein  in  a  food  material  the 
chemist  first  determines  the  percentage  of  nitrogen  and  then 
multiplies  this  by  6.25  to  obtain  the  equivalent  of  protein. 
This  is  because  proteins  contain,  on  the  average,  about  16 


COMPOSITION  OF  PLANTS 


293 


per  cent  nitrogen,  or  there  is  about  one  part  of  nitrogen  to 
every  6.25  parts  of  protein  (100  •*•  16  =  6.25).  The  method 
of  determining  the  nitrogen  consists  in  first  heating  a  weighed 
quantity  of  the  food  with  sulphuric  acid, 
which  converts  all  the  nitrogen  into  arnmo- 
nium  sulphate.  The  ammonia  from  the 
ammonium  sulphate  is  then  liberated  by 
means  of  sodium  hydroxide  (167)  and  its 
amount  determined.  The  chemist  calls  the 
material  determined  by  multiplying  the  ni- 
trogen by  6.25  crude  protein;  because  it  is 
not  quite  true  that  all  the  nitrogen  in  the 
food  is  in  the  form  of  protein. 

333.  The  non-nitrogenous  compounds 
of  plants  are  (a)  fats ;  (6)  cellulose,  or  fiber ; 
(c)  carbohydrates. 

(a)  Fats,  or  oils,  are  present  to  some  ex- 
tent in  all  parts  of  the  plant,  but  by  far  the 
larger  portion  is  found  in  the  seeds.  The 
plant  fats  are  for  the  most  part  oils,  and  the 
amount  present  varies  greatly  in  different 
plants  and  in  different  parts  of  the  same 
plant.  Wheat  contains  about  2  per  cent  of 
fat;  corn,  5  per  cent;  and  flaxseed,  35  per 
cent  or  more  of  oil.  The  roots  and  stems 
of  corn  contain  only  about  one  half  of  one 
per  cent  of  oil  or  fat.  To  determine  the 
amount  of  fat,  a  weighed  sample  of  food 
material  is  repeatedly  washed  with  ether  un- 
til all  the  fat  is  extracted ;  the  ether  is  then  evaporated  and 
the  fat  weighed.  In  practice  a  special  apparatus  (Fig.  143) 
is  used  in  which  the  same  quantity  of  ether  is  made  to  pass 


FIG.  143.  —  Appa- 
ratus used  in  deter- 
mining amount  of  fat 
or  ether  extract. 


294  ORGANIC  CHEMISTRY 

repeatedly  through  the  food  material  until  all  the  fat  is 
removed.  The  substance  extracted  from  the  food  in  this 
way  is  not  pure  fat,  or  oil,  as  the  ether  will  also  dissolve 
chlorophyll,  waxes,  and  resins  if  they  are  present.  In  the 
case  of  the  materials  ordinarily  used  as  food  for  man  and 
animals  the  amounts  of  these  substances  present  are  so  small 
as  to  cause  no  serious  error  in  the  determination;  but  to 
avoid  inaccuracy  of  statement  the  substance  determined  as 
above  is  quite  commonly  called  ether  extract  or  crude  fat. 

(b)  Cellulose.      Cellulose,  which  forms   the  walls  of   the 
plant  cells,  and  the  closely  related  woody  substances  found 
in  plants  are  commonly  called  fiber,  or  crude  fiber.     The  de- 
termination of  the  amount  of  crude  fiber  in  a  food  consists 
of  three  steps :    (1)  the  fat  is  extracted  from  the  substance 
with  ether ;    (2)  the  material  is  then  boiled  with  very  dilute 
sulphuric  acid  to  convert  the  starch  into  sugar,  which  is  then 
washed  away ;    (3)  it  is  then  boiled  with  dilute  sodium  hy- 
droxide to  dissolve  the  proteins  (317),  and  the  remaining 
material  is  washed,  dried,  and  weighed  as  crude  fiber.     The 
roots  and  stems  of  plants  contain  the  largest  amounts  of 
fiber,  as  may  be  surmised  from  their  woody  nature.     The 
seeds  usually  contain  very  little  fiber,  only  2  to  5  per  cent. 

(c)  Carbohydrates.     While  cellulose  is  strictly  speaking  a 
carbohydrate,  this  term  in  food  analysis  is  commonly  used  to 
designate  the  starches  and  sugars,  the  cellulose  being  stated 
separately  as  fiber.     Starch  is  the  most  abundant  of  the 
carbohydrates  and  is  found  principally  in  the  seeds,  roots, 
and  tubers  of  plants,  being  stored  in  those  parts  which  are 
concerned  with  new  growth.     Although  the  sugars  are  not  so 
abundant  in  nature  as  starch,  they  are  quite  widely  distrib- 
uted and  are  found  in   large  amounts  in   some  fruits  and 
vegetables  and  in  the  saps  of  sugar  cane  and  the  maple  tree. 


COMPOSITION  OF  PLANTS  295 

The  separation  and  determination  of  the  individual  carbo- 
hydrates is  a  tedious  process,  and  consequently,  since  they  all 
have  about  the  same  food  value,  they  are  usually  lumped 
together  in  the  statement  of  analysis.  In  reality  the  carbo- 
hydrates are  not  determined  at  all,  but  the  percentages  of 
water,  ash,  crude  protein,  ether  extract,  and  crude  fiber  are 
added  together;  their  sum  is  then  subtracted  from  100, 
and  the  remainder  is  the  percentage  of  carbohydrates. 
Wheat,  for  example,  contains  : 

Water 9.25  per  cent 

Ash 2.95  per  cent 

Crude  protein .13.25  per  cent 

Ether  extract 2.20  per  cent 

Crude  fiber 2.25  per  cent 

Total     !     '.     !     '.     '.     !     !     !     .     29.90  per  cent 
100  -  29.90  =  70.10  =  per  cent  of  carbohydrates. 

In  the  statement  of  analysis  of  a  feeding  stuff  for  domestic 
animals  the  expression  nitrogen-free  extract  is  used  instead  of 
carbohydrates.  In  the  analysis  of  human  foods  the  latter 
term  is  commonly  used.  In  foods  or  feeding  stuffs  of  vege- 
table origin  the  amount  of  nitrogen-free  extract,  or  carbo- 
hydrates, usually  exceeds  that  of  any  other  of  the  groups 
of  compounds. 

334.  Analysis  of  the  Corn  Plant.  If  a  number  of  samples 
of  the  corn  plant  are  taken  for  analysis  as  a  feeding  stuff  at 
the  time  the  corn  is  just  mature,  the  ayerage  composition  is 
found  to  be  about  as  follows  : 

Water 79.3  per  cent 

Ash ".„...  1.2  per  cent 

Crude  protein   ........  1 .8  per  cent 

Ether  extract 0.5  per  cent 

Crude  fiber 5.0  per  cent 

Nitrogen-free  extract 12.2  per  cent 

Total 100.0  per  cent 


293 


ORGANIC  CHEMISTRY 


The  following  table  states  the  composition  more  in  detail. 
The  numbers  show  the  percentage  of  the  various  constituents. 

Water  /  Hydrogen  8.81 
79.3    1  Oxygen     70.49 


Cora 

Plant 

100 


Dry 


'  Crude  protein       1.8 

Nitrogen    0.29 

Organic  matter 
19.5   ' 

Ether  extract       0.5 
Crude  fiber    .       5.0 

Carbon      9.05 
Oxygen      8.89 

Nitrogen-free 

Hydrogen  1.27 

.     extract  .     .     12.2 

Chlorine    .     .     0.04 

Potassium      .     0.33 

Phosphorus    .     0.05 

Calcium    .     .     0.12 

Magnesium    .     0.09 

Ash  .     .     1.2 

Iron      .     .     .     0.02 

Sulphur     .     .     0.01 

Sodium     .     .    0.03 

Silicon  .     .     .     0.11 

Oxygen     .     .     0.40 

It  is  worth  noting  that  this  table  shows  that  over 
per  cent  of  the  green  plant  is  composed  of  three  elements, 
carbon,  hydrogen,  and  oxygen,  while  all  other  elements 
combined  make  up  only  about  1-J  per  cent  of  its  weight. 


EXERCISES 

Ex.  205.  Recall  an  experiment  that  shows  the  presence  of  water 
in  plants.  About  how  much  water  do  growing  plants  contain  ?  Which 
contain  the  larger  percentage  of  water,  old  or  young  plants  ?  Is  there 
any  water  in  cured  hay  and  grains  ?  How  is  the  amount  of  water  in  a 
plant  determined  in  the  laboratory  ?  (Note  to  the  teacher.  If  a  good 
balance  and  water  oven  are  available  the  student  should  make  a  deter- 
mination of  the  amount  of  water  in  a  green  plant.) 

Ex.  206.  Burn  some  plant  material  in  a  porcelain  dish.  Stir  the 
material  until  the  ash  is  nearly  white.  What  is  included  in  the  ash 


COMPOSITION   OF  PLANTS  297 

of  the  plant  ?  How  is  the  exact  amount  of  ash  in  the  plant  determined  ? 
What  is  meant  by  the  dry  matter  of  the  plant  ?  Do  the  chemical  ele- 
ments exist  in  the  plant  in  the  same  compounds  in  which  they  are 
found  in  the  ash  ?  Are  the  ash  elements  evenly  distributed  in  all  parts 
of  the  plant  ?  Which  part  contains  the  least  ash  ?  The  most  ash  ? 

Ex.  207.  What  is  meant  by  the  organic  matter  of  the  plant  ?  How 
does  it  differ  from  dry  matter?  Recall  an  experiment  to  show  the 
presence  of  proteins  in  plants.  Which  class  of  proteins  is  present  in 
plants  in  largest  quantity  ?  In  what  part  of  the  plant  are  the  proteins 
most  abundant  ?  What  is  protoplasm  ?  Why  are  proteins  so  impor- 
tant to  the  plant  ?  How  is  crude  protein  determined  in  the  laboratory  ? 
Why  is  the  nitrogen  multiplied  by  6.25  ? 

Ex.  208.  Place  a  tablespoonful  of  corn  meal  or  ground  flaxseed  in  a 
small  bottle  and  add  an  ounce  of  ether.  Cork  the  bottle  and  shake  it 
at  intervals  for  an  hour.  Filter  the  contents  through  a  dry  filter  into 
a  glass  dish  and  place  it  in  the  open  window  until  the  ether  evapo- 
rates. (Caution.  Do  not  handle  the  ether  near  a  flame.)  Did  the 
ether  extract  any  fat  from  the  meal  ?  How  is  fat  in  foods  determined 
in  the  laboratory  ?  Which  part  of  the  plant  usually  contains  the  most 
fat? 

Ex.  209.  Place  about  one  gram  of  ground  straw  or  hay  in  a  beaker 
and  add  200  cc.  of  water  and  20  drops  of  sulphuric  acid.  Boil  on  a 
sand  bath  20  minutes.  Allow  the  material  to  settle  and  pour  off  the 
liquid.  Add  100  cc.  of  water  and  when  the  material  again  settles  pour 
off  as  before.  Now  add  200  cc.  of  water  and  4  cc.  of  the  sodium 
hydroxide  solution  of  the  laboratory  (10  %),  boil  20  minutes,  and  wash 
as  before.  The  material  left  in  the  beaker  is  crude  fiber. 

Ex.  210.  What  is  the  crude  fiber  of  the  plant  ?  How  is  the  per- 
centage of  crude  fiber  determined?  What  parts  of  the  plant  contain 
the  most  fiber?  Are  the  other  carbohydrates  of  the  plant  determined 
directly?  How  are  they  calculated?  What  does  "nitrogen-free  ex- 
tract "  mean?  Discuss  the  composition  of  the  corn  plant. 


CHAPTER   XXXVI 
CHEMISTRY   OF  PLANT   GROWTH 

335.  Seeds.     Most  of  the  crops  grown  by  farmers  and 
gardeners  are  raised  from  seeds.     A  careful  examination  of 
a  seed  shows  that  it  consists  of  an  embryo  plant  (Fig.  144  pi) 
surrounded  by  reserve  food  materials  in  the  form  of  mineral 
matter  and  nitrogenous  and  non-nitrogenous  organic  com- 
pounds.     An  analysis  would  show  that 
while  the  total  amount  of  ash  in  the 
seed   is   small   it   is  especially  high  in 
phosphorus,  potassium,  and  magnesium 

—  ash  elements  that  are  of  great  im- 
portance in  the  nutrition  of  the  young 
plant.  The  non-nitrogenous  part  con- 
sists in  most  seeds  largely  of  starch,  with  some  oil  and  cel- 
lulose, and  a  little  sugar  and  gums.  In  such  seeds  as  flax, 
rape,  mustard,  and  cotton  seed,  oil  is  the  principal  non- 
nitrogenous  substance.  Oil  seeds  are,  as  a  rule,  small  in  size 
but  concentrated  in  food  materials.  The  nitrogenous  com- 
pounds of  the  seed  are  mainly  in  the  form  of  insoluble  pro- 
teins, such  as  the  glutens  of  the  cereals.  Some  other  pro- 
teins, as  albumins,  are  present  in  small  quantities  as  well 
as  traces  of  amino-compounds. 

336.  Germination  of  Seeds.     When  a  seed  is  planted  in 
warm,  moist  soil  it  first  absorbs  moisture  and  swells,  then 
bursts  the  seed  coat,  and  begins  to  sprout   (Fig.  145).      It 

298 


CHEMISTRY  OF  PLANT  GROWTH 


299 


pushes  a  shoot  upward  and  a  root  downward,  but  until  the 
leaf  expands  and  the  root  has  fairly  entered  the  soil,  the 
young  plant  derives  no  nourishment  other  than  water, 
either  from  the  earth  or  from  the  air.  It  lives  on  the  starch, 
gluten,  mineral  matter,  and  other  compounds  contained 
in  the  seed.  The  seed,  therefore,  acts  as 
a  storehouse  of  concentrated  food  to 
nourish  the  plant  until  it  is  able  to  draw 
its  nutrition  from  external  sources.  But 
the  substances  found  in  the  seed  are  for 
the  most  part  insoluble;  hence  they 
must  undergo  a  chemical  change  before 
they  can  be  taken  up  into  the  sap  and 
conveyed  along  the  vessels  of  the  young 
shoot  they  are  destined  to  feed.  It 
is  so  arranged  in  nature  that  when  the 
seed  first  sprouts,  there  is  produced  at  the 
base  of  the  germ  a  small  quantity  of  a 
white  soluble  substance  called  diastase. 
This  substance  acts  upon  the  starch,  making  it  soluble  in  the 
sap,  which  is  thus  enabled  to  take  it  up  and  convey  it  just 
as  it  is  wanted,  to  the  shoot  or  to  the  root.  The  starch  is 
thus  converted  into  dextrine  and  maltose  (309).  In  the  oily 
seeds  the  mucilage  and  oil  take  the  place  of  starch  in  nourish- 
ing the  young  sprout.  The  oil  is  first  decomposed  into  glyc- 
erin and  fatty  acids  (303),  and  these  substances  are  finally 
converted  into  carbohydrates. 

As  the  sap  ascends,  the  dextrin  from  the  starch  is  further 
changed  into  sugar.  This  sugar  is  later  changed  into  cellu- 
lose, or  woody  fiber  of  the  stem  and  leaf.  By  the  time  that 
the  food  contained  in  the  seed  is  exhausted,  the  plant  is  able 
to  live  by  its  own  exertions,  at  the  expense  of  air  and  soil. 


FIG.  145.  — Seedlings 
of  corn. 


300  APPLIED  CHEMISTRY 

In  like  manner  the  insoluble  protein  compounds  in  the 
seed  are  converted  into  soluble  forms  similar  to  the  peptones. 
Some  of  the  soluble  proteins  are  even  broken  down  into 
amines,  which  are  then  in  a  condition  to  be  transported 
through  the  plant  tissue  and  used  as  building  material. 
These  compounds,  when  they  reach  the  place  where  they 
are  used,  are  reconstructed  into  proteins. 

337.  Conditions  Necessary  for  Germination.  These  re- 
quirements are  the  presence  of :  (1)  moisture,  (2)  oxygen, 
and  (3)  heat.  If  seeds  are  kept  dry,  they  will  not  sprout. 
They  will,  however,  retain  their  vitality  for  a  long  time,  and 
advantage  is  taken  of  this  fact  in  the  storage  of  seeds 
for  future  use.  In  the  case  of  agricultural  plants,  germina- 
tion is  best  effected  when  the  soil  is  moist  but  not  wet. 

Likewise  seeds  which  are  kept  under  the  proper  conditions 
of  moisture  and  temperature  will  not  germinate  if  they  are 
not  supplied  with  oxygen.  Seeds  often  fail  to  grow  because 
they  are  planted  at  too  great  a  depth  to  obtain  the  needed 
oxygen  from  the  air.  The  necessity  of  oxygen  for  germina- 
tion may  be  shown  by  a  simple  experiment.  When  seeds  are 
put  into  water  those  which  float  are  usually  the  only  ones  that 
germinate.  Those  which  sink  cannot  germinate  for  lack  of 
oxygen.  If  a  current  of  air  is  kept  passing  through  the  water 
all  the  seeds  will  germinate.  Seeds  kept  under  the  proper 
conditions  of  moisture  and  temperature  in  bottles  in  which 
the  air  is  replaced  by  any  inert  gas,  such  as  hydrogen  or  car- 
bon dioxide,  will  not  germinate. 

Finally  if  seeds  are  supplied  with  sufficient  moisture  and  air 
but  kept  cold,  germination  will  not  occur.  Seeds  sown  dur- 
ing cold  weather  often  remain  some  weeks  before  sprouting, 
while  those  sown  in  warm  weather  may  germinate  in  a  few 
days.  Seeds  of  different  plants  vary  in  the  amount  of  heat 


CHEMISTRY   OF  PLANT  GROWTH 


301 


they  need  for  germination.  Wheat,  oats,  and  peas  will 
sprout  while  the  ground  is  quite  cool  and  can  be  sown  early 
in  the  spring.  Corn  requires  more  heat  than  oats  ;  while  soy 
beans,  cucumbers,'  melons,  and  cotton  need  still  more 
warmth  in  the  soil.  Hence  the  farmer  and  gardener  arrange 
the  time  of  planting,  waiting  until  the  soil  has  the  proper 
temperature  before  planting  the  various  kinds  of  seeds. 

338.  Carbon  Dioxide  Exhaled  during  Germination.     The 
sprouting  of  the  seed  starts  the  hitherto  dormant  cells  into 
active  life  and  growth,  and  one  result  of 

all  life,  whether  animal  or  vegetable,  is 
the  production  of  carbon  dioxide  through 
respiration  (Fig.  146)  .  This  accounts  for 
the  need  of  oxygen  during  germination. 
The  production  of  carbon  dioxide  is  due 
to  the  oxidation  of  some  of  the  carbon 
compounds  of  the  seeds. 

339.  Roots,  Bulbs,  and  Tubers.    Some 

•i  i  .     i  i      xi        r»  showing  that  germinating 

plants  do  not  bear  seeds  the  first  year  seeds  produce  carbon 
but  go  into  a  resting  stage  during  the  ' 
winter  and  produce  seeds  the  following  year.  Such  plants 
are  called  biennial.  They  store  the  material  needed  to  start 
growth  the  second  year  in  enlarged  fleshy  roots,  like  the 
beet  ;  in  underground  stems  or  tubers,  like  the  potato  ;  or 
in  enlarged  stalks  called  bulbs,  like  the  onion.  The  food 
materials  in  these  storage  organs  are  similar  to  those  found 
in  the  seeds  ;  but  they  are  not  in  such  a  dry  and  concentrated 
form.  The  chemical  changes  which  these  compounds  un- 
dergo when  growth  begins  in  the  spring  are  similar  to  those 
which  occur  during  the  germination  of  the  seeds. 

340.  Manufacture   of    Carbohydrates.      If  the   plantlet 
produced  by  the  seed  is  kept  in  the  dark,  it  remains  color- 


FIG.  146.—  Apparatus 

inating 

carbon 


302  APPLIED  CHEMISTRY 

less  and  grows  until  the  food  which  was  stored  in  the  seed  is 
exhausted.  Under  normal  conditions,  however,  the  leaves 
of  the  plantlet  become  green  before  the  food  stored  in  the 
seed  is  completely  exhausted,  and  the  green  plant  has  the 
power  of  preparing  its  own  food  from  the  simple  compounds 
absorbed  from  the  soil  and  the  atmosphere. 

The  green  coloring  material  found  in  the  leaves  is  called 
chlorophyll,  and  a  microscopic  examination  of  the  leaf  shows 
that  it  is  contained  in  small  grains  called  chlorophyll  bodies  or 
chloroplasts ,  which  are  imbedded  in  the  protoplasm  of  the  leaf 
cell.  The  chemistry  of  chlorophyll  is  little  understood,  but 
it  is  of  utmost  importance  to  the  plant  because  its  pres- 
ence enables  the  protoplasm  of  the  leaf  to  produce  all  the 


Stomata 


A 

FIG.  147.  —  Leaf  structure.     A,  upper  surface.    B,  under  surface.     C,  cross 

section. 

organic  compounds  of  the  plant.  Of  special  interest  is  the 
manner  in  which  the  plant  manufactures  its  carbohydrates. 
The  carbon  dioxide  of  the  air  enters  the  leaves  through  the 
tiny  openings  or  stomata,  which  are  found  on  the  under  side, 
and  passes  into  the  air  spaces  between  the  cells,  and  finally 
into  the  cells  themselves. 

In  the  cell  the  carbon  dioxide  unites  with  the  water 
which  the  plant  has  absorbed  from  the  soil  and  forms  car- 
bonic acid.  Under  the  action  of  chlorophyll  and  daylight 


CHEMISTRY   OF  PLANT  GROWTH  303 

the  carbonic  acid  probably  breaks  up  into  formaldehyde  and 
oxygen : 

H2CO3  ->-  CH2O  +  2O. 

The  oxygen  is  given  off  through  the  cell  walls  into  the  air 
spaces  and  passes  out  through  the  stomata  into  the  atmos- 
phere. The  formaldehyde  is  then  probably  almost  in- 
stantly changed  to  glucose,  thus  : 

6  CH2O  ->-  C6Hi2O6. 

The  glucose  manufactured  in  this  way  is  then  transported 
to  that  part  of  the  plant  needing  new  material  for  growth, 
where  it  is  changed  into  cellulose,  starch,  oil,  or  other  of  the 
numerous  plant  compounds.  But  during  the  daytime  the 
glucose  is  produced  more  rapidly  than  it  can  be  transported, 
and  the  cells  would  be  clogged  with  soluble  food  if  it  were 
not  changed  to  an  insoluble  form  for  temporary  storage. 
The  plant,  therefore,  has  the  power  of  changing  the  glucose 
into  starch,  thus : 

C6H12O6  ->•  C6HioO5  +  H2O. 

At  night,  when  no  carbonaceous  matter  is  being  formed, 
the  starch  is  changed  back  to  glucose  or  other  soluble  com- 
pounds and  is  transported  to  other  parts  of  the  plant.  By 
morning  all  the  starch  has  disappeared  from  the  leaves.  In 
testing  for  starch,  the  leaf  is  first  boiled  to  kill  the  protoplasm 
and  then  treated  with  alcohol  to  extract  the  chlorophyll. 
After  this  it  is  placed  in  a  dilute  solution  of  iodine,  which  gives 
a  violet  coloration  to  any  starch  which  may  be  present. 

341.  Daylight  Necessary  for  Carbon  Fixation.  It  has 
already  been  stated  (105)  that  daylight  is  necessary  to  enable 
the  plant  to  utilize  the  carbon  of  the  carbon  dioxide.  The 
light  waves  absorbed  by  the  chlorophyll  supply  the  proto- 


304 


APPLIED   CHEMISTRY 


FIG.  148.  —  Exclusion  of  light  from 
part  of  a  leaf. 


plasm  with  the  energy  necessary  to  enable  it  to  split  off  the 
oxygen  from  the  carbonic  acid  (340) .  This  process  of  build- 
ing carbohydrates  from  water  and  carbon  dioxide  is  called 

photosynthesis;  it  is  a  chemical 
synthesis  (32)  by  means  of  light. 
That  light  is  necessary  for  the 
formation  of  starch  can  be  shown 
by  covering  part  of  a  leaf  with 
some  opaque  substance  early  in 
the  morning  (Fig.  148),  and  in 
the  afternoon  picking  the  leaf  and 
testing  for  starch.  It  will  be 
found  that  no  starch  is  present  in 
the  part  that  was  kept  dark,  but  that  starch  is  abundant  in 
the  rest  of  the  leaf.  The  common  garden  nasturtium  is  an 
excellent  plant  for  this  experiment,  but  any  other  rapidly 
growing  plant  will  do.  If  a  few  leaves  are  tested  early  in  the 
i  morning  they  will  generally  be  found 
to  contain  no  starch,  while  those 
tested  toward  evening  will  show 
starch  in  abundance.  Plants  kept 
in  the  dark  will  give  no  test  for 
starch  in  their  leaves,  and  if  allowed 
to  remain  in  the  dark  too  long  they 
even  lose  their  green  color. 

The  light  of  the  electric  arc  and, 
indeed,  any  white  light,  can  furnish 
energy  for  carbon  fixation,  and  it 
has  been  suggested  that  plants 
might  be  made  to  grow  more  rapidly  if  supplied  with  light 
at  night.  This  has  been  tried  in  the  greenhouse ;  but  it  has 
been  found  that  while  the  pl'ants  in  the  houses  lighted  at 


FIG.  149.  —The  same  leaf  tested 
with  iodine,  showing  absence  of 
starch  in  part  excluded  from  light. 


CHEMISTRY  OF  PLANT  GROWTH  305 

night  do  grow  more  rapidly,  the  extra  growth  does  not  repay 
the  extra  expense  of  lighting. 

At  the  time  of  the  most  color  in  plants,  there  is  the  greatest 
cell  activity  and  the  largest  amount  of  plant  tissue  is  being 
produced.  When  a  plant  ripens,  the  decline  of  activity 
of  the  cells  may  be  observed  by  the  change  in  the  color  of  the 
plant.  In  corn  the  lower  joints  of  the  stalk  turn  yellow 
first,  indicating  that  growth  and  activity  have  ceased  in 
those  parts.  Then  the  upper  leaves  become  yellow,  and 
finally  the  husk  becomes  yellow  and  inactive.  Chloro- 
phyll is  one  of  the  principal  agents  taking  an  active  part  in 
plant  growth,  and  whenever  it  is  destroyed,  plant  growth  is 
checked. 

As  the  atmosphere  contains  only  3  parts  in  10,000  of 
carbon  dioxide,  it  may  be  thought  that  a  larger  amount  of 
this  gas  would  enable  the  plant  to  make  a  greater  growth.  It 
has  been  possible,  indeed,  with  plants  in  small  inclosures, 
to  increase  the  growth  by  adding  carbon  dioxide  to  the  air. 
There  is  every  reason  to  believe,  however,  that  plants  grown 
in  the  open  never  suffer  for  lack  of  it  and  that  the  size  of  the 
crop  is  always  limited  by  some  other  factor,  and  never 
because  of  an  insufficient  supply  of  carbon  dioxide  (105-107). 

342.  Respiration.  Every  living  cell  must  breathe  during 
the  entire  period  of  its  active  life.  Growing  plants,  therefore, 
breathe  or  respire  during  all  of  the  twenty-four  hours. 
Through  respiration  the  plant  takes  in  oxygen  and  gives  off 
carbon  dioxide.  The  statement  so  often  seen  that  "during  the 
night  plants  take  in  oxygen  and  breathe  out  carbon  dioxide, 
and  in  the  daytime  take  in  carbon  dioxide  and  breathe  out 
oxygen,"  is  not  strictly  true.  The  process  of  photosynthesis 
should  not  be  confused  with  respiration.  The  latter  occurs 
day  and  night,  while  the  former,  which  is  strictly  a  manu- 
EV.  CHEM. — 20 


306  APPLIED  CHEMISTRY 

facturing  process  and  has  nothing  to  do  with  breathing,  takes 
place  only  during  daylight.  It  is  true  that  the  amount  of 
oxygen  given  off  during  photosynthesis  is  so  much  greater 
than  that  absorbed  by  respiration  that  the  latter  process  is 
obscured  during  the  daytime  by  the  former.  The  oxygen 
evolved  during  six  hours  of  active  carbon  fixation  is  as  much 
as  would  be  absorbed  by  the  process  of  respiration  in  twenty- 
four  hours.  It  is  evidently  true,  then,  that  plants  decrease 
the  amount  of  carbon  dioxide  in  the  air  during  daylight,  but 
that,  like  animals,  they  add  to  it  during  the  night. 

343.  Changes  in  the  Carbohydrates.     The  change  of  the 
sugar  of  the  plant  sap  into  cellulose,  or  woody  fiber,  is  more 
or  less  observable  in  all  plants.     When  they  are  growing 
fastest  the  sugar  is  most  abundant,  not,  however,  in  those 
parts  that  are  actually  growing,  but  in  those  which  convey 
the  sap  to  the  growing  parts.     Thus  the  sugar  of  the  ascend- 
ing sap  of  the  maple  disappears  in  the  leaf  and  extremities  of 
the  twig,  and  sugar  cane  is  sweet  only  a  certain  distance  above 
the  ground,  up  to  where  the  new  growth  is  proceeding.     In 
the  ripening  of  the  ear,  the  sweet  taste  so  perceptible  in  young 
grain   gradually   diminishes,    and   finally   disappears.     The 
sugar  of  the  sap  is  here  changed  into  the  starch  of  the  grain, 
which  is  destined,  when  the  grain  sprouts,  to  be  reconverted 
into  sugar  for  the  nourishment  of  the  growing  grain. 

In  the  ripening  of  fruits  a  different  series  of  changes  pre- 
sents itself.  The  fruit  is  at  first  tasteless,  then  becomes 
sour,  and  at  last  sweet.  In  this  case,  either  the  acid  of  the 
unripe  fruit  is  changed  into  the  sugar  of  the  ripened  fruit,  or 
some  of  the  other  constituents  of  the  fruit  are  converted  into 
sugar  which  disguises  the  acid. 

344.  Manufacture  of  Protein.     Carbohydrates  are  not  the 
only  chemical  compounds  that  are  produced  in  the  leaf.     A 


CHEMISTRY   OF  PLANT   GROWTH 


307 


very  important  work  of  the  leaf  is  the  production  of  proteins, 
the  most  complex  compounds  known.  How  these  compounds 
are  manufactured  is  not  known.  Starting  with  the  carbo- 
hydrates, and  the  nitrogen,  sulphur,  and  phosphorus  secured 
from  the  soil,  the  leaf  cell  builds  up  the  very  complex  protein 
molecule.  Other  parts  of  the  plant  manufacture  protein  to 
some  extent ;  but  its  production  goes  on  most  actively  in  the 
leaf,  from  which  it  is  transported  to  other  parts  of  the  plant. 
345.  Some  Plants  Cannot  Manufacture  Food.  Plants  not 
possessing  chlorophyll  are  not  able  to  decompose  carbonic 
acid  and  produce  carbohydrates.  Such  plants  must  have 
their  carbonaceous  and  nitrogenous  foods  prepared  for  them. 
Mushrooms  and  Indian  pipe  are  examples  of  such  plants. 
They  feed  upon  the  compounds  formed  by  the  decaying  or- 
ganic matter  in  the  soil.  The  fungi  that  grow  on  decaying 
trunks  of  trees  also  belong  to  this  class  of  plants.  Some 
colored  plants,  like  the  dodder,  are  parasites  and  live  on  the 
juices  of  other  plants. 

EXERCISES 

Ex.  211.  Rub  50  kernels  of  barley  in  a  mortar  with  a  .little  water. 
Filter  and  test  the  water  with  Fehling's  solution  for  reducing  sugar. 
What  is  the  result  ?  Put  50  other  barley 
seeds  between  two  thicknesses  of  moist 
cotton  flannel  and  place  these  between 
two  plates  as  shown  in  Fig.  150.  Stand 
the  plates  in  a  warm  place  for  two  or 
three  days  or  until  the  sprouts  are  about 
half  an  inch  high.  Rub  the  germinated 
seeds  in  the  mortar  as  above  and  test  with 
Fehling's  solution.  What  is  the  result? 
What  happened  to  the  starch  of  the  seed 
during  germination?  To  what  was  this 
change  due?  Do  similar  changes  take 
place  in  the  proteins  of  the  seed  ? 


FIG.  150.  —  A  seed  tester. 


308  APPLIED  CHEMISTRY 

Ex.  212.  What  conditions  are  necessary  for  the  germination  of 
seeds  ?  Boil  some  water  and  when  it  is  cold  place  it  in  a  glass  tumbler 
and  drop  a  few  radish  or  wheat  seeds  on  the  surface.  Note  if  there  is 
any  difference  in  the  seeds  which  float  and  those  which  sink.  Explain. 

Ex.  213.  (Teacher)  Place  an  inch  of  moist  sawdust  in  the  bottom 
of  three  eight-ounce  wide-mouth  bottles,  and  drop  a  few  radish  or  other 
seeds  on  the  sawdust.  Cork  one  bottle  tightly,  and  set  it  aside.  Fill 
another  bottle  with  carbon  dioxide  by  downward  displacement  and  cork 
it  tightly.  Fill  the  third  bottle  with  oxygen  by  downward  displace- 
ment and  cork  it.  Watch  the  bottles  for  several  days  and  note  any 
difference  in  germination.  Is  oxygen  necessary  for  germination  ?  Is 
heat  also  necessary  ?  Dp  seeds  vary  in  the  amount  of  warmth  neces- 
sary for  germination? 

Ex.  214.  (Teacher)  Place  a  vial  of  clear  limewater  in  a  wide- 
mouth  bottle  and  surround  the  vial  with  well-soaked  seeds  (Fig.  146). 
Cork  the  bottle  tightly  and  observe  the  limewater.  What  change 
takes  place  ?  How  do  you  account  for  it  ? 

Note.  As  a  check  to  the  above  another  bottle  might  be  arranged  in 
the  same  way  except  that  perfectly  dry  seeds  should  be  used. 

Ex.  216.  Pick  some  leaves  from  a  vigorously  growing  plant  in  the 
afternoon.  Boil  them  in  water  for  a  few  minutes  and  then  immerse 
them  in  hot  alcohol  to  extract  the  chlorophyll.  Dip  the  leaves  in  a 
very  dilute  solution  of  iodine.  Is  there  any  evidence  of  starch  ?  How 
did  the  starch  get  there  ?  Explain  the  production  of  carbohydrates  in 
the  leaf. 

Ex.  216.  Cover  half  of  a  leaf  while  on  the  plant  on  both  sides  with 
black  paper  or  tin  foil  one  afternoon  and  pick  the  leaf  the  next  afternoon 
and  test  for  starch.  Is  there  any  difference  in  the  two  parts  of  the  leaf  ? 
Explain.  Pick  leaves  in  the  early  morning  and  in  the  early  evening 
from  the  same  plant.  Test  for  starch  in  the  usual  way.  Does  electric 
light  have  the  same  effect  upon  plant  growth  as  sunlight  ?  Is  there 
sufficient  carbon  dioxide  in  the  atmosphere  for  plant  growth  ? 

Ex.  217.  Is  it  correct  to  say  that  "  plants  breathe  out  oxygen  during 
the  daytime  "  ?  Explain  what  really  happens.  What  is  respiration  ? 

Ex.  218.  Are  proteins  manufactured  in  the  leaf?  Can  all  plants 
manufacture  their  own  food?  How  do  the  fungi  obtain  their  food? 
How  do  the  parasites  obtain  theirs? 


CHAPTER  XXXVII 

CHEMISTRY    OF   PLANT    GROWTH    (Continued} 

346.  Importance  of  Water  to  the  Plant.  Analysis  of  the 
corn  plant  (334)  shows  that  it  contains  nearly  80  per  cent 
water.  There  is  also  found  in  the  organic  matter  an  amount 
of  hydrogen  and  oxygen  equal  to  about  10  per  cent  of  the 
entire  plant,  and  it  has  been  shown  that  these  elements  are 
derived  from  water  (340). 

It  is  evident,  then,  that  the  plant  obtains  about  90  per 
cent  of  its  substance  from  water.  This  statement,  however, 
gives  but  little  idea  of  the  amount  of  water  required  by  the 
plant  during  its  period  of  growth.  The  leaves  of  the  grow- 
ing plant  are  constantly  exhaling  water.  This  process  is 
known  as  transpiration.  Very  large  amounts  of  water  are 
transpired  by  plants. 

Experiments  have  shown  that  while  producing  one  pound 
of  dry  matter  the  plant  gives  off  from  300  to  500  pounds 
of  water  by  transpiration.  A  fair  crop  of  corn  transpires 
during  the  growing  season  at  least  900  tons  of  water  to  the 
acre,  or  an  amount  of  water  that  would  be  equal  to  a  layer 
that  would  cover  the  entire  acre  about  8  inches  deep.  The 
table  that  appears  on  the  next  page  gives  the  average  amount 
of  water  transpired  by  some  of  the  common  farm  crops,  as 
determined  at  the  Wisconsin  Experiment  Station. 

309 


310 


APPLIED  CHEMISTRY 


AVERAGE  AMOUNT  OF  WATER  USED   TO  PRODUCE 
ONE  POUND  OF  DRY  MATTER 


CROP 

WATER 

Barley                 ...          .... 

461  1  pounds 

Oats               

503  9  pounds 

270.9  pounds 

Clover       

576.6  pounds 

Peas 

477  2  pounds 

Potatoes 

385.1  pounds 

347.  How  the  Plant  Obtains  Its  Water.  All  the  water 
used  by  the  plant  is  absorbed  from  the  soil  by  the  plant  roots. 
The  growing  ends  of  the  rootlets  are 
clothed  with  numerous  root  hairs 
which  are  responsible  for  the  absorp- 
tion of  the  water  needed  by  the  plant. 
The  manner  in  which  the  root  hairs 
absorb  water  from  the  soil  may  be 
illustrated  by  a  simple  experiment. 
Tie  a  piece  of  moist  animal  mem- 
brane (hog's  bladder  will  serve  the 
purpose)  over  the  end  of  a  thistle 
tube  (Fig.  151),  and  when  dry  cover 
the  edge  of  the  membrane  with 
melted  paraffin,  to  make  the  joint 
watertight.  Fill  the  enlarged  part 
of  the  thistle  tube  with  a  strong  solu- 
tion of  sugar  or  salt,  and  place  the 
tube  in  a  glass  of  water,  sinking  it 
until  the  level  of  the  liquid  in  the 
tube  stands  at  the  same  height  as 
that  in  the  glass.  In  a  short  time 


Fl°- 


CHEMISTRY   OF  PLANT  GROWTH  311 

the  water  begins  to  rise  in  the  tube,  and  in  time  flows 
over  the  top  of  the  tube.  The  water  passes  through  the 
membrane  by  osmotic  action,  or  osmosis.  Whenever  a  mem- 
brane like  this  one  separates  a  strong  solution  from  a  weak  one, 
there  is  a  decided  movement  of  water  from  the  weaker  solu- 
tion to  the  stronger,  which  tends  to  con- 
tinue until  the  liquid  is  of  the  same  con- 
centration on  both  sides  of  the  membrane. 

Under  the  microscope  the  root  hairs 
(Fig.  152)  are  seen  to  be  long  tubelike 
bladders.  These  root  hairs  are  filled 
with  cell  sap,  which  is  a  much  more 
concentrated  solution  than  soil  water ; 
hence  the  water  passes  into  the  root 
hairs  by  osmotic  action.  Once  in  the 
root  hairs  the  water  passes  on  to  the  root 
and  stem  and  leaf,  to  be  utilized  in  FlG  152.*_  Root  ^  of 
growth  or  given  off  by  transpiration.  young  radish  plants. 

348.  Functions  of  Water  in  the  Plant.  Water  is  impor- 
tant to  the  plant  in  several  different  ways.  It  is  first  of  all 
the  most  essential  plant  food  in  the  sense  that  it  furnishes  the 
material  for  90  per  cent  of  the  weight  of  the  plant.  Water 
is  necessary  to  dissolve  the  plant  food  in  the  soil  and  enable 
it  to  enter  the  plant,  as  will  be  noted  later.  It  is  also  neces- 
sary for  the  movement  of  food  within  the  plant.  The  food 
materials  absorbed  by  the  roots  and  those  manufactured  in 
the  leaves  can  be  transported  to  the  different  parts  of  the 
plant  where  they  are  needed  only  when  in  solution  in  water. 
Water  performs  an  important  function  in  controlling  the 
temperature  of  the  plant.  Chemical  processes  in  the  plant 
cell  produce  heat,  and  the  excess  of  heat  is  removed  by 
transpiration  of  water  through  the  leaves. 


312 


APPLIED   CHEMISTRY 


Water  is  needed  also  to  give  stiffness  or  rigidity  to  the  more 
succulent  parts  of  the  plant.  This  fact  is  shown  by  the 
drooping  or  wilting  of  plants  during  the  hot  hours  of  the  day 
when  the  water  is  not  furnished  by  the  roots  with 
sufficient  rapidity  to  repair  the  loss  by  evapora- 
tion from  the  leaves.  In  the  experiment  with 
the  thistle  tube  (Fig.  151)  it  was  noted  that  the 
water  was  raised  to  some  height  in  the  tube,  and 
consequently  the  walls  of  the  tube  must  have 
been  subjected  to  some  internal  pressure.  The 
experiment  may  be  performed  in  another  way. 
Tie  a  piece  of  bladder  (A)  over  one  end  of  a  glass 
tube  (Fig.  153)  and  fill  the  tube  with  a  strong 
sugar  solution.  Over  the  other  end  fasten  a  piece 
of  thin  sheet  rubber  (B),  and  place  the  bladder 
end  in  a  vessel  of  water.  After  some  time  it  will 
be  found  that  the  water  absorbed  has  created 
sufficient  pressure  to  distend  the  rubber,  and  if 
the  rubber  is  punctured  with  a  pin  the  water 
will  be  ejected  with  some  force.  The  pressure 
FIG  153—  created  by  osmosis  in  this  way  is  called  osmotic 
Apparatus  to  pressure.  When  the  plant  cells  can  obtain  all 

demonstrate    * 

osmotic  pres-  the  water  they  need,  they  are  kept  distended 
and  rigid  by  osmotic  pressure.  When  the  water 
is  removed  faster  than  it  is  absorbed,  the  osmotic  pressure 
is  decreased,  the  cell  loses  its  rigidity  and  finally  the  whole 
plant  droops  or  wilts.  The  protoplasm  does  its  work 
properly  only  when  the  cell  is  turgid,  and,  therefore,  wilting 
is  always  injurious  to  the  plant. 

349.  How  the  Plant  Obtains  Its  Mineral  Matter.  The 
mineral  matter,  or  ash,  of  the  plant  is  obtained  from  the  soil. 
Small  quantities  of  the  different  mineral  substances  used  by 


CHEMISTRY   OF  PLANT  GROWTH  313 

the  plant  are  found  dissolved  in  the  soil  water.  These  dis- 
solved materials  diffuse  into  the  root  hairs  by  osmosis  and 
then,  like  the  water,  pass  on  to  root  and  stem  and  leaf  to  be 
utilized  in  plant  growth.  If  none  of  these  substances  were 
used  by  the  plant,  this  diffusion  would  continue  until  there 
was  the  same  strength  of  each  of  the  mineral  substances  in 
the  plant  sap  and  in  the  soil  water.  When  the  plant  uses  one 
of  these  substances,  more  will  come  into  the  root  hairs  in 
order  to  preserve  the  equilibrium.  Thus  those  substances 
which  are  needed  by  the  plant  must  come  in  as  long  as  the 
soil  can  furnish  them  in  a  soluble  form. 

350.  Essential  and  Non-essential  Elements.  Although 
the  plant  contains  nitrogen  and  the  nine  ash  elements  which 
it  obtains  from  the  soil,  it  does  not  follow  that  all  of  these  ele- 
ments are  necessary  to  its  growth.  To  determine  which  ele- 
ments are  essential,  plants  are  grown  in  sand  or  by  the  water 
culture  method  in  such  a  way  that  they  are  supplied  with  all 
the  elements  occurring  in  plants,  with  the  exception  of  the 
one  element  under  investigation.  If  the  plant  grows  to 
maturity,  the  missing  element  is  deemed  non-essential;  it 
the  plant  fails  to  develop,  that  particular  element  is  con- 
sidered to  be  essential.  These  experiments  indicate  that 
nitrogen,  potassium,  calcium,  magnesium,  iron,  sulphur,  and 
phosphorus  are  absolutely  essential  to  plant  growth.  Toward 
chlorine,  silicon,  and  sodium  plants  seem  to  be  indifferent, 
as  they  can  grow  to  maturity  in  the  absence  of  these  elements. 

Another  important  fact  discovered  in  these  experiments  is 
that  one  chemical  element  cannot  be  substituted  for  another 
in  plant  growth,  even  when  both  elements  are  similar  in 
chemical  properties.  In  the  laboratory,  for  example,  sodium 
and  potassium  compounds  are  much  alike  in  their  action, 
and  one  may  be  used  in  place  of  the  other  in  many  reactions ; 


314 


APPLIED   CHEMISTRY 


but  sodium  cannot  take  the  place  of  potassium  as  a  plant 

food  (Fig.  154). 

351.   Roots  Dissolve  Mineral  Substances.     The  plant  not 

only  absorbs  what  is 
already  soluble  in  the 
soil  water,  but  it  is 
capable  of  making  sol- 
uble small  quantities 
of  the  insoluble  sub- 
stances which  are  pres- 
ent in  the  soil  and 
which  may  be  needed 
for  plant  food.  The 
plant  accomplishes 
this  result  by  means  of 
substances  excreted  by 
the  roots.  If  a  plant 


FIG.  154.  —  Showing  the  effect  of  sodium  (A) 

and  potassium  (*)  on  plant  growth.  Jg     gr()wn 

sawdust  placed  on  a  piece  of  polished  marble,  it  will  be 
found  that  the  prints  of  the  roots  are  distinctly  shown  on  the 
surface  of  the  marble 
(Fig.  155).  Pieces  of 
limestone  in  the  soil 
often  show  markings  due 
to  the  solvent  action  of 
plant  roots. 

352.  The  Nitrogen  of 
Plants.  This  element  is 
largely  derived  from  the 
nitrates  in  the  soil  which  enter  the  root  hairs  by  osmosis. 
The  plants  known  as  the  legumes  obtain  part  of  their  nitrogen 
from  the  nodules  found  on  their  roots.  These  are  the 


FIG.  155.  —  Marble  corroded  by  bean  roots. 


CHEMISTRY   OF  PLANT  GROWTH  315 

homes  of  bacteria  that  have  the  power  of  fixing  the  nitrogen 
of  the  air.  They  cause  the  nitrogen  to  combine  with  other 
substances  to  form  compounds  which  can  be  utilized  as  a 
source  of  nitrogen  for  the  manufacture  of  protein.  Legumes 
use  the  nitrates  in  the  soil  when  they  can  obtain  them,  and 
only  fix  atmospheric  nitrogen  when  the  supply  of  nitrate  is 
insufficient. 

353.  Functions  of  the  Elements  in  Plant  Growth.  Car- 
bon, oxygen,  and  hydrogen  are  constituents  of  all  the  organic 
compounds  manufactured  by  the  plants.  These  three  ele- 
ments constitute  about  98.5  per  cent  of  the  mature  plant. 

Nitrogen  is  a  necessary  constituent  of  the  proteins,  which 
play  an  important  part  in  the  formation  of  protoplasm, 
chlorophyll,  and  other  compounds.  Abundance  of  nitrogen 
in  the  soil  is  indicated  by  the  bright  green  color  of  the  leaves. 

Potassium  is  one  of  the  most  important  elements  in  plant 
growth.  It  is  present  in  greatest  amount  in  the  leaves  and 
the  actively  growing  parts  of  the  plant.  Apparently  it 
aids  in  the  production  of  carbohydrates,  such  as  starch  and 
sugar.  Abundance  of  potassium  is  said  to  increase  the 
amount  of  sugar  in  fruits  and  in  such  roots  as  the  sugar  beet. 

Calcium  takes  a  prominent  part  in  the  production  of  new 
tissue  and  in  the  development  of  strong  cell  walls  and  nu- 
merous root  hairs.  It  serves  also  as  a  base  to  precipitate 
the  poisonous  oxalic  acid  which  is  formed  by  cell  activities. 

Magnesium  assists  in  the  formation  of  chlorophyll  and  the 
proteins.  It  is  necessary  to  seed  formation,  and  seeds  grown 
with  an  insufficient  supply  of  magnesium  are  often  sterile. 

Phosphorus  is  a  necessary  constituent  of  some  proteins. 
It  is  found  mainly  in  the  seeds.  It  increases  the  yield  and 
hastens  the  ripening  of  grain.  Many  proteins  insoluble  in 
water  are  soluble  in  the  presence  of  phosphorus  compounds, 


316 


APPLIED  CHEMISTRY 


Iron  occurs  in  the  smallest  amount  of  any  of  the  ash 
elements  but  is  always  present  in  plants.  It  is  necessary  for 
the  formation  of  chlorophyll. 

Sulphur  is  a  necessary  constituent  of  most  proteins.  It  is 
also  a  part  of  some  of  the  flavoring  oils,  such  as  those  found 
in  mustard,  onions,  cabbage,  and  horseradish. 


EXERCISES 

Ex.  219.     Invert  a  wide-mouth  bottle  over  a  potted  plant,  first  cover- 
ing the  soil  with  waxed  paper.     (Fig.  156.)     What  is  the  source  of  the 
moisture  that  collects  ?     How  much  water  do  plants 
transpire  in  producing  a  pound  of  dry  matter  ?    How 
much  water  is  transpired  by  an  acre  of  corn  ? 

Ex.  220.  (Teacher)  Perform  the  experiment 
described  in  347.  How  does  it  illustrate  the  move- 
ment of  water  into  the  plant  ?  Germinate  some 
radish  seeds  between  two  layers  of  moist  cloth 
(Fig.  150)  and  examine  the  root  hairs  under  the  mi- 
croscope. Are  they  well  designed  to  absorb  water  ? 
Ex.  221.  (Teacher)  Perform  the  experiment 
illustrated  in  Fig.  153.  How  does  water  give  rigid- 
ity to  the  plant?  Why  do  plants  wilt?  Is  tur- 
gidity  of  the  cell  necessary  ?  What  are  some  of  the 
other  functions  of  water  in  the  plant? 

Ex.  222.     How  does  the  plant  obtain  its  mineral 
matter?     Describe    an    experiment    to   determine 
which  mineral  elements  are  necessary.     Name  the  essential  elements. 

Ex.  223.  (Teacher)  Place  a  slab  of  polished  marble  in  a  small  box 
and  cover  with  an  inch  of  moist  sand.  Plant  seeds  of  peas  or  beans  and 
keep  watered.  After  growth  has  proceeded  for  some  time  wash  the 
marble.  Is  there  proof  that  the  roots  dissolved  the  marble  ? 

Germinate  some  radish  seeds  between  pieces  of  blue  litmus  paper. 

(Fig.  150.)    What  effect  do  the  root  hairs  have  on  the  litmus  ?    Is  it 

probable  that  roots  have  power  of  dissolving  mineral  food  in  the  soil  ? 

Ex.  224.     What  is  the  source  of  the  nitrogen  used  by  the  plant? 

Discuss  the  functions  of  the  different  elements  used  in  plant  growth. 


FIG.  156.— Exper- 
iment showing  that 
water  is  given  off 
from  the  leaves  of 
plants. 


CHAPTER  XXXVIII 
ENZYMES  — DIGESTION—  FERMENTATION 

354.  Enzymes.  In  studying  the  germination  of  seeds 
(336)  it  was  found  that  a  substance  called  diastase  which  has 
the  power  of  changing  starch  into  maltose  is  formed  in  the 
seed.  Diastase  belongs  to  a  group  of  substances  known  as 
enzymes.  They  are  the  products  of  living  cells  but  are  not 
themselves  living  things.  Very  little  is  known  of  the  true 
nature  of  enzymes  or  of  their  chemical  action,  as  none  of  them 
have  been  obtained  in  a  state  of  absolute  purity.  They  are 
very  complex  substances  of  a  protein  character.  They  are 
soluble  in  water  and  glycerin  but  are  insoluble  in  alcohol. 
For  the  purpose  of  study  an  enzyme  is  obtained  by  pulveriz- 
ing the  tissue,  extracting  the  enzyme  with  glycerin,  and  then 
precipitating  it  by  the  addition  of  alcohol.  The  material 
obtained  in  this  way  is  not  a  pure  enzyme,  but  contains  the 
enzyme  in  a  concentrated  form.  Diastase  prepared  from 
malt  in  this  way  shows  in  a  marked  manner  the  property 
of  transforming  starch  into  maltose. 

The  enzymes  are  specific  in  their  action.  Diastase,  for 
example,  converts  starch  into  maltose,  but  it  has  no  effect 
on  other  substances ;  and  in  like  manner  each  enzyme  acts 
on  one  particular  substance,  producing  in  it  a  definite  change. 
The  enzymes  behave  like  catalytic  agents  in  that  they  them- 
selves undergo  no  permanent  change,  but  under  proper  con- 
ditions can  cause  an  almost  indefinite  amount  of  chemical 

317 


318  APPLIED   CHEMISTRY 

change  in  the  substance  upon  which  they  act.  Thus  one 
part  of  diastase  can  change  at  least  2000  parts  of  starch  into 
maltose  without  any  of  the  enzyme  itself  being  destroyed. 

355.  Malt  is  a  good  example  of  the  commercial  utilization 
of  enzymic  action.     Malt  is  produced  from  barley  by  soaking 
the  grain  in  water  for  some  time  and  then  spreading  it  in  thick 
layers  upon  the  floor  of  a  warm  room.     Germination  takes 
place,  and  when  the  sprouts  are  about  one  half  inch  long,  the 
grain  is  heated  sufficiently  to  kill  the  embryo,  and  then  dried. 
The  sprouts  are  removed  and  sold  as  a  cattle  feed  under  the 
name  of  malt  sprouts.     The  remaining  grain  is  known  as  malt. 
The  germinating  process  makes  the  diastase  active,  and  if  the 
malt  is  now  placed  in  warm  water,  the  starch  of  the  grain  is 
converted  into  maltose,  which  may  be  changed  by  the  action 
of  yeast  into  alcohol,  as  is  done  in  the  manufacture  of  beer, 
whisky,  and  ordinary  alcohol.     Since  the  amount  of  diastase 
in  the  barley  is  capable  of  changing  a  large  amount  of  starch 
into  maltose,  other  starchy  materials,  such  as  corn  and  rice, 
are  frequently  added  to  the  "  mash."    The  residual  grain, 
after  all  the  starch  has  been  made  soluble  and  thus  removed, 
is  dried  and  sold  as  cattle  feed  under  the  name  of  dried 
brewers'  grains,  or  dried  distillers'  grains,  according  to  whether 
it  comes  from  the  brewery  or  the  distillery. 

356.  Digestion.     The    process    by   which   the    insoluble 
food  materials  are  made  soluble  so  they  can  be  absorbed  into 
the  blood  of  animals  is  called  digestion.     It  is  in  large  part, 
if  not  wholly,  the  result  of  the  action  of  several  enzymes. 
Digestion  takes  place  in  various  parts  of  the  alimentary  canal, 
notably  in  the  mouth,  stomach,  and  small  intestines. 

357.  Digestion  in  the  Mouth.     The  food  is  first  ground  into 
fine  particles  by  mastication  so  that  the  digestive  juices  can 
act  upon  it  to  better  advantage.     During  this  process  the  food 


ENZYMES,   DIGESTION,   FERMENTATION         319 


is  thoroughly  mixed  with  the  saliva,  which  contains  an  en- 
zyme known  as  ptyalin.  This  enzyme  is  much  like  diastase 
in  its  action  and  changes  the  starch  of  the  food  into  maltose. 


2  C6H10O5 

starch 


H2O 


C12H220U. 

maltose 


The  normal  saliva  is  slightly  alkaline,  and  ptyalin  can  act 
only  in  an  alkaline  solution.  No  constituents  of  the  food 
other  than  starch  are  acted  upon  in  the  mouth,  and  not  all 
the  starch  is  rendered  soluble.  The  food  material,  thor- 
oughly moistened,  passes  into  the  stomach,  where  the  next 
change  takes  place. 

358.  Digestion  in  the  Stomach.  In  man,  the  horse,  and 
the  pig  there  is  but  one  stomach,  but  in  the  ruminants,  like 
cattle  and  sheep, 
there  are  four  stom- 
achs (Fig.  157)  or 
rather  four  com- 
partments to  the 
stomach.  Animals 
of  the  latter  class 
chew  the  cud.  The 
food  is  passed  from 
the  mouth  into  the 
first  and  second 
compartments  of 
the  stomach,  and  is  then  forced  back  into  the  mouth  for 
further  mastication  ;  then  it  is  swallowed  again  and  passed 
through  the  third  stomach  into  the  fourth  for  final  digestion. 
The  storage  in  the  first  and  second  stomach  and  the  re- 
peated mastication  of  the  food  merely  serve  to  grind  the 
food  completely  and  to  prepare  it  thoroughly  for  digestion. 


FlO.  157  — The  four  main  divisions  of  a  ruminant's 
stomach. 


320  APPLIED  CHEMISTRY 

In  this  way  these  animals  are  able  to  digest  fibrous  material 
to  a  much  greater  extent  than  other  animals,  such  as  the 
horse.  The  true  gastric  digestion  in  the  case  of  ruminants 
takes  place  in  the  fourth  stomach. 

The  glands  in  the  wall  of  the  stomach  secrete  a  digestive 
fluid,  called  gastric  juice,  which,  unlike  the  saliva,  is  acid 
in  reaction  and  contains  about  0.2  per  cent  of  hydrochloric 
acid.  It  also  contains  two  enzymes  —  pepsin  and  rennin. 
The  pepsin  acts  upon  the  insoluble  proteins  and  gradually 
converts  them  into  peptones,  which  are  soluble  and  diffusible. 
Pepsin  acts  only  in  an  acid  solution.  Rennin,  the  other 
enzyme  of  the  gastric  juice,  acts  on  the  casein  of  milk,  causing 
it  to  coagulate  or  curdle,  a  process  the  necessity  of  which  is 
not  understood.  The  coagulated  casein  is  then  dissolved 
by  the  pepsin.  Rennin  is  especially  abundant  in  the  stomach 
of  the  young,  and  the  commercial  rennet  used  in  cheese  mak- 
ing is  prepared  from  the  stomachs  of  young  calves.  No 
food  constituents  save  the  proteins  are  acted  upon  by  the 
stomach  enzymes,  and  they  are  not  completely  digested  but 
in  part  pass  on  into  the  small  intestine. 

359.  Digestion  in  the  Intestine.  When  the  food  reaches 
the  small  intestine  it  comes  in  contact  with  the  intestinal  and 
pancreatic  juices.  These  fluids  have  an  alkaline  reaction 
and  contain  several  enzymes. 

Trypsin  is  an  enzyme  that  acts  upon  the  proteins  which 
escape  digestion  in  the  stomach.  It  is  more  energetic  in  its 
action  than  is  pepsin.  It  acts  only  in  an  alkaline  solution. 

Amylopsin  is  a  pancreatic  enzyme  that  acts  on  starch, 
converting  it  into  maltose,  and  is  more  energetic  in  its  action 
than  ptyalin. 

Steapsin,  or  lipase,  is  an  enzyme  that  acts  upon  the  fats 
of  the  food.  It  hydrolyzes  fats  into  glycerin  and  fatty  acids 


ENZYMES,   DIGESTION,   FERMENTATION         321 

(298),  which  is  probably  the  first  step  in  their  digestion. 
Steapsin  and  amylopsin  are  active  only  in  alkaline  solution. 

360.  Bile  is  a  fluid  secreted  by  the  liver  and  discharged 
into  the  small  intestine  together  with  the  pancreatic  juice. 
It  is  a  thin  liquid,  with  a  bitter  taste,  and  is  very  alkaline.     It 
varies  in  color  from  greenish-yellow  to  reddish-brown,  the 
shade  depending  on  the  animal.     No  enzymes  have  been  dis- 
covered in  the  bile,  but  its  presence  decidedly  increases  the 
power  of  the  pancreatic  enzymes. 

The  various  food  materials  that  have  been  changed  into 
soluble  compounds  by  the  action  of  the  digestive  enzymes 
are  absorbed  from  the  small  intestines  and  ultimately  find 
their  way  into  the  blood  to  be  transported  to  the  part  of  the 
body  where  they  are  needed.  The  part  of  the  food  that  is 
not  changed  into  soluble  compounds  passes  on  into  the  large 
intestine  and  is  finally  excreted  in  the  feces,  which,  there- 
fore, represent  in  a  general  way  the  undigested  food. 

361.  Other  Enzymes.     The  enzymes  mentioned  in  this 
chapter  are  only  a  few  of  the  many  whose  existence  is  known, 
and  new  ones  are  being  constantly  added  to  the  list.     The 
pineapple  is  known  to  contain  an  enzyme  that  digests  pro- 
tein.    Some  enzymes  bring  about  oxidation  by  causing  the 
union  of  substances  with  the  oxygen  of  the  air.       Such 
enzymes  are  called  oxidases.     The  brown  coloration  which  ap- 
pears on  the  cut  surface  of  an  apple  or  other  fruit  is  said  to 
be  caused  by  the  action  of  an  oxidase.     The  enzymes  studied 
herein  assist  in  breaking  complex  substances    into   simple 
bodies,  but  there  are  undoubtedly  enzymes  that  produce 
opposite  results.     The  synthesis  of  starch  in  the  leaves  and 
the  production  of  proteins,  as  well  as  many  other  processes 
of  the  plant  and  animal  body  are  thought  by  some  investiga- 
tors to  be  dependent  upon  the  presence  of  enzymes. 

EV.  CHEM — 21 


322  APPLIED   CHEMISTRY 

362.  Fermentation  is  a  term  applied  to  changes  in 
organic  substances  that  are  brought  about  through  the 
growth  of  microscopic  plants,  such  as  yeast,  molds,  or 
bacteria.  The  production  of  alcohol  by  the  action  of  yeast 
is  the  best-known  example  of  fermentation.  The  souring  of 
milk,  the  change  of  cider  to  vinegar,  and  the  decay  of  or- 
ganic substances  are  examples  of  fermentation  caused  by 
bacteria.  It  was  formerly  thought  that  the  growing  cells 
themselves  produced  the  chemical  changes  incident  to  the 
fermentation,  but  many  investigators  now  believe  that  the 
yeasts,  or  bacterial  cells,  produce  enzymes  that  are  really 
responsible  for  the  chemical  changes  in  the  fermenting  mate- 
rial. It  was  found  that  a  sample  of  yeast,  for  instance,  that 
was  ground  in  such  a  way  as  to  rupture  every  cell  and  thus 
destroy  its  life,  still  had  the  power  of  producing  alcoholic 
fermentation.  It  is  now  said  that  yeast  contains  at  least 
two  enzymes :  namely,  invertase,  which  has  the  power  of 
inverting  cane  sugar,  and  zymase,  which  converts  invert  sugar 
or  maltose  into  alcohol  and  carbon  dioxide. 

EXERCISES 

Ex.  225.  Crush  20  malted  barley  grains  in  a  mortar.  Transfer  to 
a  test  tube,  add  15  cc.  of  water,  and  allow  the  mixture  to  stand  twenty- 
four  hours.  Filter  off  the  solution  and  add  to  a  bottle  containing 
100  cc.  of  starch  solution  made  as  follows  :  rub  one  gram  of  starch  with 
10  cc.  of  water  until  smooth  and  then  pour  on  100  cc.  of  boiling  water 
and  allow  the  liquid  to  cool.  Allow  the  mixture  to  stand  another 
twenty-four  hours.  Test  a  portion  of  it  for  starch.  State  the  result. 
Test  another  portion  with  Fehling's  solution.  State  the  result.  What 
change  has  taken  place  in  the  starch?  What  caused  this  change? 
What  is  the  active  principle  of  the  malt  ?  What  are  enzymes  ?  Are 
they  specific  in  their  action?  Explain.  Are  they  catalytic  agents? 
What  commercial  use  has  the  enzymic  action  of  malt?  What  are 
dried  brewers*  grains? 


ENZYMES,   DIGESTION,   FERMENTATION         323 

Ex.  226.  Fill  a  test  tube  one  third  full  of  your  saliva.  If  the  saliva 
does  not  flow  freely  chew  a  piece  of  paraffin.  Add  to  the  saliva  an  equal 
volume  of  starch  solution  prepared  as  in  the  last  exercise.  Place  the  test 
tube  in  a  cup  of  water  at  blood  heat  for  an  hour.  Test  a  portion  of  mix- 
ture for  starch.  If  the  starch  has  not  all  disappeared,  allow  the  mixture 
to  stand  another  hour.  What  change  has  the  saliva  caused  in  the 
starch  ?  How  did  you  test  for  starch  ?  What  is  the  enzyme  of  the  sa- 
liva ?  How  is  the  food  affected  in  the  mouth  ?  Is  the  saliva  acid,  or 
alkaline,  or  neutral  ? 

Ex.  227.  What  enzymes  are  found  in  the  stomach  ?  Review  Exer- 
cise 200.  Repeat  that  experiment,  substituting  a  tablespoonful  of 
ground  lean  meat  for  the  white  of  the  egg.  State  the  result.  Does 
pepsin  act  best  in  an  acid  or  alkaline  solution  ?  Compare  with  ptyalin. 
What  action  does  the  rennin  of  the  gastric  juice  have  on  milk  ? 

Ex.  228.  What  three  enzymes  are  found  in  the  intestines?  State 
the  action  of  each.  What  effect  does  the  bile  have  on  digestion  ? 

Ex.  229.  Explain  what  is  meant  by  fermentation.  Give  examples. 
Do  enzymes  play  any  part  in  fermentations  ?  Are  enzymes  concerned 
in  any  processes  other  than  digestion  and  fermentations  ?  What  causes 
the  brown  coloration  of  the  cut  surface  of  an  apple?  (Note.  If  an 
apple  is  cut  in  two  and  placed  in  a  bottle  containing  sulphur  dioxide 
for  a  short  time,  the  cut  surface  will  not  turn  brown  when  exposed  to  the 
air  as  the  sulphur  dioxide  destroys  the  enzyme  oxidase.)  Are  enzymes 
ever  supposed  to  take  part  in  building  up  complex  compounds  ? 


CHAPTER  XXXIX 
PRINCIPLES    OF   NUTRITION 

363.  Uses  of  Food.     The  animal  body  uses  the  foods  for 
the  following  purposes  :  (1)  to  repair  the  waste  of  the  system  ; 
(2)  to  supply  heat ;    (3)  to  furnish  motion ;    (4)  to  provide 
the  materials  needed  for  the  increase  of  flesh  by  growth  or 
fattening;   (5)  to  make  special  products,  such  as. milk,  eggs, 
feathers,  wool,  and  hair.     The  animal  body  may  in  many 
ways  be  compared  to  the  gasoline  engine  or  other  "  prime 
motor."     The  gasoline  engine  requires  two  things  for  its 
operation  :    (1)  sufficient  repair  material  to  keep  its  working 
parts  in  running  order,  and  (2)  a  supply  of  fuel  in  proportion 
to  the  work  to  be  done.     The  same  two  things  are  needed  by 
the  animal ;  namely,  repair  material  and  fuel. 

364.  Repair  Material.     The  repair  material  for  any  ma- 
chine must  be  of  the  same  kind  as  that  of  which  the  machine 
is  made.     Protein  is  the  characteristic  ingredient  of  the  ani- 
mal mechanism ;  for  the  muscles  with  which  the  animal  does 
its  work  are  largely  composed  of  protein,  and  this  material 
is  broken  down  and  destroyed  at  a  fairly  uniform  rate  by  the 
operation  of  the  animal  machine.     Since  the  bodily  machin- 
ery is  running  all  the  time,  whether  any  external  work  is  being 
done  or  not,  this  loss  is  going  on  continually.     The  body 
differs  from  the  engine  in  being  self-repairing,  but  as  the  ani- 
mal does  not  have  the  power  to  manufacture  proteins,  it  is 
absolutely  dependent  for  its  repair  material  on  the  proteins 
of  its  food.     This  protein  is  needed  for  two  purposes. 

324 


PRINCIPLES   OF  NUTRITION  325 

First,  it  is  necessary  for  repair  material  in  the  strict  sense ; 
namely,  to  make  good  the  wear  and  tear  of  the  body  machin- 
ery. The  amount  needed  for  the  purpose  is  small,  and  is  not 
materially  greater  when  the  animal  is  doing  work  than  when 
it  is  not.  A  second  purpose  for  which  protein  and  ash  are 
needed  in  the  growing  animal  is  to  furnish  the  material  for 
enlarging  its  body.  Protein  is  necessary  also  to  enable  the 
animal  to  manufacture  milk,  eggs,  hair,  wool,  and  other 
special  products ;  for  all  of  these  contain  proteins,  which  the 
animal  must  obtain  from  its  food. 

365.  Food  as  a  Source  of  Repair  Material.     The  value  of 
a  food  or  feeding  stuff  as  a  source  of  protein  evidently  de- 
pends in  the  first  place  on  the  amount  of  protein  which  it 
contains.    Beans,  containing  23  per  cent  of  protein,  are,  other 
things  being  equal,  a  better  source  of  protein  than  corn,  which 
contains  only  10  per  cent.     Since  the  protein  of  the  food  must 
be  capable  of  being  digested  by  the  animal,  the  most  valuable 
source  of  repair  material  is  the  food  or  feeding  stuff  contain- 
ing the  largest  amount  of  digestible  protein  (368). 

366.  Fuel  or  Energy  Materials.     The   animal  requires 
heat  to  maintain  the  body  temperature  and  energy  to  do 
its  work.    The  source  of  this  heat  and  energy  is  the  food 
which  the  animal  digests,  and  which  is  oxidized  in  its  body. 
Since  the  animal  machinery  is  running  continually,    it   re- 
quires a  constant  supply  of  fuel  material,  the  amount  neces- 
sary depending  upon  the  amount  of  work  done.     This  con- 
sists chiefly  of  the  carbohydrates  and  fats   of  the  food, 
although  if  more  protein  is  fed  than  is  required  for  repair 
and  construction  purposes,  it  may  be  used  as  fuel.     The  un- 
necessary  use  of  protein    as  fuel   material  is  wasteful,  as 
protein  is  ordinarily  much  more  expensive  than  are  carbo- 
hydrates and  fats. 


326 


APPLIED  CHEMISTRY 


367.  Fuel  Value,  or  Energy  Value,  of  Foods.  TKe  differ- 
ent foods  and  food  constituents  are  not  all  of  equal  value  as 
sources  of  energy.  It  will  be  found  convenient  to  have  a 
means  of  comparing  the  different  foods  and  feeds,  and  the  best 
basis  for  such  a  comparison  is  the  relative  energy  values  of 
these  materials .  Anything  which  has  the  capacity  to  do  work 
is  said  to  possess  energy.  The  fuel  of  the  engine  and  the  food 
of  the  animal  possess  energy,  since  they  enable  the  engine  or 
the  body  to  do  work.  This  energy  is  stored  up  as  latent 

energy,  and  when  the  fuel  is 
burned  in  the  engine,  or  the  food  is 
oxidized  in  the  body,  this  latent 
energy  is  set  free  and  part  of  it  is 
converted  into  the  work,  the  rest 
escaping  as  heat.  The  value  of 
a  fuel  depends  on  the  amount  of 
this  latent  energy  it  contains,  and 
this  can  be  determined  by  burning 
the  substance  to  convert  the  latent 
energy  into  heat,  and  then  measur- 
ing the  heat  produced. 

The  fuel  value  of  a  food  is  de- 
termined by  burning  a  weighed 
quantity  of  the  food  in  a  calorim= 
eter  (Fig.  158).  This  is  a  metal  vessel  or  bomb,  which  is 
immersed  in  a  vessel  of  water.  The  heat  produced  by  the 
burning  substance  warms  the  water,  and  the  rise  in  tempera- 
ture is  determined  by  a  thermometer.  Various  units  have 
been  employed  in  measuring  heat.  Perhaps  the  oldest  and 
most  common  is  the  calorie  (spelled  with  a  small  c)  which  is 
the  amount  of  heat  necessary  to  raise  the  temperature  of  one 
gram  of  water  one  degree  centigrade.  This  unit  is  so  small 


FIG.  158.  —  A  calorimeter. 


PRINCIPLES  OF  NUTRITION 


327 


that  it  has  long  been  customary  in  discussing  foods  to  use  the 
large  Calorie  (spelled  with  a  capital  C),  which  is  equivalent 
to  1000  small  calories,  or,  in  other  words,  is  the  amount  of 
heat  required  to  raise  the  temperature  of  one  kilogram  (1000 
grams)  of  water  one  degree.  In  discussing  the  feeding  of 
farm  animals  even  the  large  Calorie  is  found  to  be  an  incon- 
veniently small  unit,  and  some  writers  make  use  of  the  therm, 
which  is  equivalent  to  1000  large  Calories ;  that  is,  it  is  the 
amount  of  heat  required  to  raise  the  temperature  of  1000 
kilograms  of  water  one  degree  centigrade. 

A  pound  of  either  carbohydrates  or  protein  when  burned 
produces  1860  large  Calories  of  heat,  or  1.86  therms.  A 
pound  of  fat,  which  is  a  much  more  concentrated  fuel,  pro- 
duces 4225  Calories,  or  4.23  therms  of  heat.  It  will  be  seen 
that  the  pound  of  fat  produces  approximately  two  and  one 
fourth  times  as  much  heat  as  an  equal  weight  of  carbohydrates 
or  protein.  The  following  examples  serve  to  illustrate  the 
great  variation  in  the  energy  value  of  different  foods : 


FOOD 

ENERGY  VALUE  PER 
POUND 

Calories 

C  abb  a  fire 

170 

Potatoes     

380 

Eeers  . 

720 

Wheat  flour     

1660 

Cheese        

1990 

Butter         

3600 

It  has  been  shown  that  only  the  protein  that  is  digested 
is  of  any  use  to  the  animal  body,  and  it  is  equally  true  that 
only  the  digested  part  of  the  food  can  supply  the  animal  with 


328  APPLIED  CHEMISTRY 

energy.  The  undigested  part,  which  passes  off  in  the  excre- 
ment, represents  that  part  of  the  energy  that  cannot  be  uti- 
lized by  the  animal  machine.  To  determine  how  much  energy 
a  food  will  furnish,  it  is  necessary  to  know  what  proportion 
of  the  food  is  actually  digested ;  and  that  can  be  determined 
only  by  experiments  with  animals. 

•  368.  Digestion  Experiments.  The  digestibility  of  a  food 
is  determined  by  a  carefully  conducted  digestion  experiment. 
The  animal,  or  man,  is  fed  for  a  few  days  on  the  food  to  be 
investigated,  the  food  having  been  analyzed  to  determine  its 
content  of  protein,  fat,  carbohydrates,  fiber,  and  other 
constituents;  and  the  amount  eaten  is  carefully  recorded. 
The  f eces,  which  represent  the  undigested  part  of  the  food,  are 
collected,  weighed,  and  analyzed.  The  difference  between 
the  undigested  nutrients  and  the  total  amounts  in  the  food 
consumed  is  the  amount  digested,  which  is  then  calculated 
on  a  percentage  basis.  For  example,  suppose  the  analysis 
of  the  food  shows  that  the  animal  consumed  four  pounds  of 
protein  during  the  experimental  period,  and  that  the  feces 
contained  one  pound  of  protein. .  The  animal,  then,  was  able 
to  digest  three  pounds  of  protein  out  of  the  four  pounds  con- 
sumed. In  other  words,  three  fourths,  or  75  per  cent,  of  the 
protein  was  digestible.  In  the  same  way  the  percentage  of 
digestibility  may  be  worked  out  for  the  fats,  ash,  and  each  of 
the  other  nutrients  of  the  food.  Some  authors  use  the  ex- 
pression coefficient  of  digestibility  to  designate  the  percentage 
of  a  nutrient  which  can  be  digested.  In  the  above-assumed 
example  the  coefficient  of  digestibility  for  protein  is  75. 

369.  Available  Energy  of  Foods.  Only  that  part  of  the 
food  which  is  digested  can  furnish  energy  to  the  animal  ma- 
chine, and  not  all  of  this  energy  can  be  utilized  by  the  body. 
Some  of  the  digested  portion  of  the  food  fails  to  undergo 


PRINCIPLES  OF  NUTRITION  329 

complete  oxidation  in  the  body  and  is  excreted  in  the  licjuid 
excrement.  The  energy  that  can  be  utilized  is  called  the 
available  energy  of  the  food.  It  is  determined  by  finding  the 
total  number  of  Calories  in  the  food,  and  subtracting  there- 
from the  caloric  value  of  the  feces  as  well  as  the  caloric  value 
of  the  compounds  found  in  the  liquid  excrement. 

370.  Net  Energy  of  Foods.  In  the  process  of  digestion, 
particularly  of  coarse  fodders,  a  part  of  the  energy  of  the 
food  is  used  to  separate  the  real  fuel  material  from  the 
relatively  large  proportion  of  useless  material  in  the  food. 
The  energy  thus  used  up  in  carrying  on  the  process  of  diges- 
tion is  not  available  for  other  purposes.  It  is  possible  to 
determine  the  approximate  amount  of  energy  required  by 
the  animal  in  order  to  chew  the  food  and  digest  it,  and  this 
amount  subtracted  from  the  available  energy  gives  the  net 
energy  of  the  food.  In  the  case  of  coarse  fodders  a  large  part 
of  the  available  energy  is  used  in  digestion,  leaving  compara- 
tively little  net  energy.  Less  energy  is  required  to  digest 
grains,  and  thus  a  larger  proportion  of  their  energy  can  be 
used  fqr  other  purposes  by  the  body.  The  total  fuel  value 
of  one  pound  of  timothy  hay,  for  example,  is  1751  Calories, 
but  its  net  energy  value  is  only  335  Calories.  The  total  fuel 
value  of  corn  meal  is  1709  Calories  and  its  net  energy  value  is 
888  Calories.  Therefore,  while  the  total  fuel  value  of  these 
two  substances  is  not  very  different,  there  is  a  marked  con- 
trast in  the  amount  of  net  energy  which  they  furnish. 

If  the  fuel  materials  supplied  in  the  food  are  just  adequate 
to  the  work  to  be  done,  they  are  all  burned  up  as  a  source 
of  power.  If  more  are  supplied  than  are  immediately  needed, 
the  body  is  able  to  store  the  surplus  for  future  use.  Most 
of  the  surplus  fuel  is  converted  into  fat,  which,  therefore,  is 
the  reserve  fuel  of  the  body.  In  fattening,  the  body  is  accu- 


330  APPLIED   CHEMISTRY 

mulating  a  surplus  against  future  needs.  If  the  food  later 
becomes  insufficient,  this  store  is  drawn  upon  and  the  animal 
becomes  thin.  Similarly,  in  growth  and  milk  production, 
the  animal  sets  aside  a  part  of  the  supply  of  both  repair  and 
fuel  material  in  its  food  for  its  own  growth  or  for  the  use  of 
its  young.  Man  takes  advantage  of  these  tendencies  of  the 
animal  to  store  fat  and  meat,  and  to  produce  milk,  and  di- 
verts the  resulting  products  to  his  own  use  as  repair  and 
fuel  material  for  his  own  body. 

EXERCISES 

Ex.  230.  What  five  general  uses  does  the  animal  make  of  its  food  ? 
Why  is  the  animal  body  likened  to  a  prime  motor  engine?  What 
furnishes  the  repair  material  for  the  animal  body?  What  other  use 
does'  the  animal  have  for  protein?  Does  the  value  of  food  for  repair 
depend  on  the  total  protein  or  upon  the  digestible  protein  ? 

Ex.  231.  What  are  the  chief  energy  supplying  substances  in  the 
food  ?  How  is  the  total  energy  value  of  a  food  determined  ?  What  is 
the  measure  of  heat  ?  What  is  meant  by  the  small  calorie ;  the  large 
Calorie ;  the  therm  ?  How  much  heat  is  produced  by  burning  a  pound 
of  protein  or  carbohydrate  ?  A  pound  of  fat  ?  Do  foods  varv^  greatly 
in  their  energy  value  ? 

Ex.  232.  Does  digestibility  affect  the  amount  of  energy  which 
the  food  will  supply  to  the  animal  ?  How  is  a  digestion  experiment  con- 
ducted ?  What  is  meant  by  the  available  energy  of  the  food  ?  How 
is  it  determined  ? 

Ex.  233.  What  is  meant  by  net  energy  ?  In  what  way  does  it  differ 
from  available  energy?  Can  all  the  available  energy  be  utilized  to 
do  work  ?  Explain.  Can  all  the  net  energy  be  used  to  do  work  ?  Is 
some  energy  required  to  prepare  the  food  and  to  digest  it  ?  How  does 
the  proportion  of  net  energy  from  seeds  compare  with  that  from  fodders  ? 
If  the  net  energy  supplied  is  more  than  is  used,  what  becomes  of  the  ex- 
cess ?  Can  the  animal  use  its  own  body  fat  to  supply  energy  upon  occa- 
sion ?  Is  energy  needed  to  produce  milk  and  growth  ? 


CHAPTER  XL 
FEEDING  FARM   ANIMALS 

371.  Balanced  Rations.    It  has  been  noted  that  food  sup- 
plies the  animal  with  repair  material  and  with  energy,  both  of 
which  it  needs  to  carry  on  its  various  functions.     The  amount 
of  repair  material  and  energy  required  by  the  animal  depends 
upon  the  following  factors  :  whether  the  animal  is  growing,  or 
is  working,  or  is  producing  milk.     A  ration  that  will  supply 
the  animal  with  protein  and  energy  in  just  the  proportion  in 
which  it  needs  them  is  called  a  balanced  ration.    A  knowledge 
of  the  food  requirements  of  animals  and  of  the  method  of  cal- 
culating balanced  rations  should  be  of  value  to  the  practical 
feeder. 

372.  The  maintenance  requirement  of  the  animal  is  used 
as  the  basis  for  calculating  the  balanced  ration.     Since  the 
animal  machine  cannot  be  stopped  when  it  fe  not  in  active 
use,  it  requires  a  continual  supply  of  food.     The  amount  of 
food  that  is  required  simply  to  support  the  animal  is  desig- 
nated as  the  maintenance  requirement.     It  is  the  amount 
required  simply  to  maintain  the  animal  when  it  is  doing  no 
work  and  producing  nothing.     It  represents  the  least  amount 
on  which  life  can  be  maintained.     A  large  animal  needs  more 
food  for  maintenance  than  does  a  small  one,  although  the 
difference  is  not  exactly  proportional  to  the  weight,  but  ap- 
pears rather  to  be  approximately  proportional  to  the  body 
surface  of  the  animal.     The  proper  maintenance  require- 
ments have  been  determined  by  experiment  for  different 

331 


332 


APPLIED   CHEMISTRY 


kinds  of  animals,  of  various  ages  and  weights.     The  follow- 
ing table  gives  the  figures  for  cattle  of  four  different  weights. 

MAINTENANCE  REQUIREMENTS  FOR  CATTLE 


WEIGHT 

DIGESTIBLE  PROTEIN 

NET  ENERGY 

Pounds 

Pounds 

Therms 

750 

0.40 

4.95 

850 

0.45 

5.60 

1000 

0.50 

6.00 

1250 

0.60 

7.00 

373.  Requirements  for  Growth.     The  amount  and  nature 
of  the  food  consumed  should  vary  with  the  period  of  growth 
as  well  as  with  the  size  of  the  animal.     Rations  for  young 
growing  animals  should  contain  proportionately  more  digest- 
ible protein  and  less  energy  value  than  rations  for  mature 
animals.     This  is  because  more  food  is  required  for  building 
purposes  in  the  early  stages  of  growth  than  in  the  later  stages, 
when  the  demand  is  more  for  heat  and  energy.     When  an 
excess  of  fats  and  starchy  foods  is  given  to  young  animals, 
there  is  a  tendency  to  produce  poor  muscular  tissue  and 
premature  fattening.     The  ash  of  the  food  is  also  very  im- 
portant to  young  animals,  for  it  is  during  the  growing  period 
that  the  bones  are  built  up.     A  table  showing  the  protein  and 
energy  requirement  for  growing  animals  will  be  found  at  the 
end  of  this  chapter. 

374.  Requirements  for  Work.     The  performance  of  work 
by  the  animal  calls  for  an  additional  supply  of  energy  in  the 
feed.     Animals  when  doing  medium  or  heavy  work  also 
require  more  protein  than  do  those  at  light  work. 


FEEDING  FARM  ANIMALS  333 

REQUIREMENTS  FOR  THE  WORKING  HORSE  OF  1000  POUNDS 


CHARACTER  OP  WORK 

DIGESTIBLE 
PROTEIN 

NET  ENERGY 

Pounds 

Therms 

For  liffht  work 

1  0 

9  80 

1.4 

1240 

2.0 

1600 

375.  Requirements  for  Fattening.     When  the  animal  con- 
sumes more  energy-making  foods  than  it  can  utilize,  it  stores 
the  surplus  energy  as  fat.     To  fatten  animals,  then,  they  are 
fed  abundant  rations  high  in  net  energy  value.     It  is  esti- 
mated that  about  3.5  therms  in  addition  to  the  maintenance 
requirement  are  needed  by  the  animal  for  each  pound  of  gain 
in  weight  during  the  fattening  period. 

376.  Requirements  for  Milk  Production.     Of  all  forms  of 
animal  production  that  of  milk  is  the  most  variable  and 
most  influenced  in  its  amount  by  the  feed  supply.     Milk  is 
the  natural  food  of  the  young,  and,  as  it  is  the  only  food  of 
the  very  young  animal,  it  contains  the  protein,  the  ash,  and 
the  energy  necessary  to  its  growth.     When  a  cow  is  produc- 
ing milk,  she  must  have   in  addition  to  her  maintenance 
ration  an  amount  of  food  sufficient  to  enable  her  to  put 
protein  and  energy  materials  into  her  milk.     To  produce 
a  pound  of  average  milk  requires  0.05  pound  of  digestible 
protein  and  0.3  therm  of    energy,  which  must  be  added 
to  the  maintenance  ration  for  each  pound  of  milk  the  cow 
produces. 

377.  Dry  Matter  in  Rations.     It  has  been  found  by  experi- 
ment that  it  is  necessary  for  cattle  to  have  a  certain  bulk 


334  APPLIED   CHEMISTRY 

in  their  feed.  They  do  not  thrive  so  well  if  the  feed  is  too 
concentrated,  but  on  the  other  hand  there  might  be  such 
a  thing  as  having  a  ration  which  is  too  bulky.  The  best 
indication  of  bulk  in  the  feed  is  the  dry  matter  which  it 
contains.  In  a  general  way  it  may  be  said  that  an  animal 
weighing  1000  pounds  should  be  given  from  20  to  30  pounds 
of  dry  matter  a  day,  the  exact  amount  not  being  very  impor- 
tant if  kept  within  these  limits.  On  the  farm,  where  hay  and 
fodder  are  abundant,  it  is  usually  easy  to  obtain  a  ration 
that  is  sufficiently  bulky. 

378.  The  Ash  of  the  Ration.     The  ash,  or  mineral  matter, 
of  the  feed  is  important ;  for  the  animal  could  not  live 
very  long  if  there  were  no  mineral  matter  whatever  in  the 
feed.     It  is  especially  important  to  young,  growing  animals, 
as  they  are  building  up  bones  which  are  composed  very 
largely  of  mineral  matter.     As  the  animal  grows  older,  it 
needs  less  ash  in  the  feeds,  since  the  bones  are  no  longer 
growing  in  size. 

379.  Calculating  a  Balanced  Ration.    With  the  data  of 
this  chapter  at  hand  it  is  possible  to  calculate  rations  suited 
to  the  various  needs  of  the  domestic  animals.     To  illustrate 
the   method  of  calculation,  it  is  assumed  that  a  ration  is 
needed  for  a  cow  weighing  850  pounds  and  producing  20 
pounds  of  average  milk  each  day.      The  feeds  are  to  be 
selected  from  the  table  given  at  the  end  of  this  chapter. 

By  referring  to  page  332  it  is  seen  that  a  cow  weighing 
850  pounds  requires  for  maintenance  0.45  pound  of  digestible 
protein  and  5.60  therms  of  energy.  For  the  production  of 
20  pounds  of  milk  of  average  quality  there  would  be  required 
according  to  the  figures  given  in  paragraph  376 : 

Digestible  protein  (0.05  X  20) 1  pound 

Net  energy  value   (0.3  X  20) 6  therms 


FEEDING  FARM  ANIMALS 


335 


The  total  feed  requirements  for  a  day  for  such  a  cow  are, 
therefore,  1.45  pounds  of  digestible  protein  and  11.60  therms 
of  net  energy. 

The  problem  is  to  find  a  mixture  of  feeds  that  will  give 
these  amounts  of  protein  and  energy.  As  the  coarse  feeds 
grown  on  the  farm  are  usually  the  cheapest,  they  should  be 
used  as  far  as  possible.  First,  corn  silage  and  clover  hay 
may  be  tried  for  roughage,  as  the  coarse  feeds  are  called,  and 
corn  meal  and  wheat  bran  for  the  more  concentrated  feeds. 
It  is  necessary  to  start  with  the  best  guess  possible  as  to  the 
amounts  of  each  feed  to  use  and  make  a  table  showing  the 
results  as  below : 


RATION 

DRY  MATTER 

DIGESTIBLE 
PROTEIN 

NET  ENERGY 
VALUE 

Pounds 

Pounds 

Pounds 

Therms 

5.63 

0.26 

364 

Clover  hay    6  

5.08 

.32 

208 

Corn  meal     5       ..... 

4.46 

.34 

444 

Wheat  bran  2            .... 

1.77 

20 

96 

Total 

1694 

1  12 

11  12 

A  comparison  of  these  totals  with  the  requirement  of  1.45 
pounds  of  protein  and  11.60  therms  of  energy  shows  that  the 
ration  is  slightly  low.  in  energy  and  considerably  so  in  protein. 
If  the  addition  of  some  feed  high  in  digestible  protein,  say  1^- 
pounds  of  gluten  feed,  is  made  the  ration  stands  thus  : 


RATION 

DRY  MATTER 

DIGESTIBLE 
PROTEIN 

NET  ENERGY 
VALUE 

Pounds 

Pounds 

Therms 

In  feeds  named  above    . 
In  1^  pounds  gluten  feed   . 

16.94 
1.38 

1.12 
.30 

11.12 
1.19 

Total    

18.32 

1.42 

12.31 

336 


APPLIED   CHEMISTRY 


This  ration  gives  more  nearly  the  correct  amount  of  digest- 
ible protein,  but  has  a  surplus  of  energy,  which  would  prob- 
ably tend  to  fatten  the  cow  instead  of  increasing  the  flow  of 
milk.  The  energy  in  the  ration  should  be  reduced  without 
decreasing  the  amount  of  protein.  If  one  pound  of  corn 
meal,  which  supplies  chiefly  energy,  is  omitted,  and  replaced 
by  one  half  pound  of  gluten  feed,  the  ration  is  as  follows : 


RATION 

DRY  MATTER 

DIGESTIBLE 
PROTEIN 

NET  ENERGY 
VALUE 

Pounds 

Pounds 

Pounds 

Therms 

Corn  silage 

22       .... 

563 

026 

3  64 

Clover  hay 

6 

508 

032 

208 

Corn  meal 

4  

3.56 

027 

355 

Wheat  bran 

2  

1.77 

020 

096 

Gluten  feed 

2 

1  84 

040 

1  59 

Total 

1788 

1  45 

11  82 

The  ration  now  agrees  very  closely  with  the  computed  re- 
quirements. This  example  will  serve  to  illustrate  the  method 
of  calculating  all  rations ;  for  the  same  method  will  apply  to 
the  rations  for  fattening  cattle,  for  horses,  for  sheep  and 
swine,  and  for  chickens,  if  the  standards  for  each  kind  of  ani- 
mal are  known.  By  proceeding  in  the  manner  described, 
with  a  little  patience  a  ration  corresponding  as  closely  as  is 
necessary  to  the  standard  requirements  can  be  calculated. 
Experience  makes  it  possible  to  guess  pretty  closely  the  first 
time,  and  the  computation  soon  becomes  easy. 

380.  Individuality.  The  standard  requirements,  of  course, 
are  for  average  animals,  but  it  is  well  known  that  some 
animals  require  more  feed  than  the  average  and  some  less. 
The  wise  feeder,  therefore,  uses  the  standards  with  this  fact 
in  mind,  and  in  addition  to  calculating  his  standard  ration 


FEEDING  FARM  ANIMALS 


337 


makes  an  individual  study  of  each  cow  in  his  herd,  feeding 
her  any  amounts  for  which  she  will  give  profitable  returns. 
Even  such  a  feeder,  however,  needs  the  standard  requirements 
as  a  starting  point  in  his  study. 

381.  Palatability  of  Feeds.     There  is  another  factor  in 
feeding  animals  which  is  quite  as  important  as  that  of  bal- 
ancing the  ration ;   namely,  the  matter  of  the  palatability 
of  the  ration.     In  order  to  give  the  best  results  the  food 
should  be  relished  by  the  animal.     The  experienced  feeder 
strives  to  compound  a  ration  that  carries  the  proper  propor- 
tion of  protein  and  energy  and  is  pleasing  to  the  animal's  taste. 

382.  Older  Feeding  Standards.   The  feeding  standards  that 
have  been  most  commonly  used  in  the  past  by  writers  on  the 
feeding  of  animals  are  those  known  as  the  Wolff-Lehman 
standards.     These  standards,  instead  of  being  based  on  the 
daily  requirements  of  the  animal  for  digestible  protein  and 
energy,  are  based  on  the  theory  that  the  animal  must  have 
a  given  weight  of  dry  matter  each  day,  together  with  a  defi- 
nite amount  of  the  three  digestible  nutrients  —  protein,  car- 
bohydrates, and  fat.     The  following  table  gives  a  few  of 
the  feeding  standards  according  to  the  Wolff-Lehman  tables  : 

DAILY  REQUIREMENT  OF  DIGESTIBLE  NUTRIENTS  FOR 
EACH  1000  POUNDS  LIVE  WEIGHT  OF  ANIMAL 


ANIMAL 

DRY 

MATTER 

PROTEIN 

CARBOHY- 
DRATES 

FAT 

Pounds 

Pounds 

Pounds 

Pounds 

Cows  giving  22  pounds  of  milk 
daily        

29 

2.5 

13.0 

0.5 

Fattening  cattle  

30 

2.5 

150 

0.5 

Sheep               

23 

1.5 

120 

0.3 

Horses,  medium  work   .     .     . 
Fattening  swine                  . 

24 
36 

2.0 

45 

11.0 
250 

0.6 
0.7 

EV.    CHEM. 22 


338  APPLIED   CHEMISTRY 

The  method  of  calculating  a  ration  according  to  these 
standards  is  exactly  the  same  as  the  one  described  on  page 
335,  except  that  in  the  case  of  the  Wolff-Lehman  standards 
there  are  four  factors  to  be  balanced,  while  in  the  other  case 
only  two  items,  protein  and  energy,  are  considered.  In  the 
case  of  the  Wolff-Lehman  standards,  the  best  possible  guess 
is  made  as  to  the  feeds  that  will  fit  the  standard,  and  then 
others  are  added  or  subtracted  from  the  ration,  as  described 
in  the  foregoing  example,  until  a  mixture  is  obtained  that 
agrees  very  closely  with  the  amounts  of  dry  matter,  protein, 
carbohydrates,  and  fat  as  stated  in  the  standard.  These 
older  standards  are  being  replaced  by  those  based  on  pro- 
tein and  energy.  Tables  giving  all  the  Wolff-Lehman 
standards,  as  well  as  the  percentages  of  the  different  di- 
gestible nutrients  in  the  common  feeding  stuffs,  may  be 
found  in  the  larger  works  on  the  feeding  of  farm  animals. 

383.  The  nutritive  ratio  of  a  feed  or  a  ration  is  the  pro- 
portion between  the  digestible  protein  and  the  sum  of  the 
digestible  carbohydrates  and  fat  contained  therein.  To  find 
the  nutritive  ratio  the  fat  is  multiplied  by  2.25,  because 
it  has  2.25  times  the  food  value  of  the  carbohydrates,  and 
the  result  is  added  to  the  carbohydrates.  The  sum  is  di- 
vided by  the  digestible  protein,  the  quotient  being  the  nutri- 
tive ratio.  Thus,  the  standard  for  a  horse  at  medium 
work  calls  for  2.0  pounds  digestible  protein,  11.0  pounds 
carbohydrates,  and  0.6  pound  of  fat. 
.6X2.25  =  1.350;  1.350  +  11.0  =  12.35;  12.35^2.0  =  6.17 

The  nutritive  ratio,  therefore,  is  1  to  6.17. 

Recent  investigations  indicate  that  the  ratio  between  pro- 
tein and  the  other  nutrients  is  not  so  important  as  it  was  first 
thought  to  be,  provided  that  the  animal  is  supplied  with 
sufficient  repair  material  or  protein. 


FEEDING   FARM  ANIMALS 


339 


TABLES:  ESTIMATED  REQUIREMENTS  PER  DAY  AND  HEAD 
FOR   GROWING  ANIMALS 


CATTLE 


SHEEP 


AGE 

Months 


LlVEWT. 

Pounds 


DIGESTI- 
BLE 

PKOTEIN 
Pounds 


NET 
ENERGY 


Therms 


AGE 

Months 


LIVE  WT. 
Pounds 


DIGESTI- 
BLE 

PROTEIN 
Pounds 


NET 
ENERGY 


Therms 


12 

18 
24 


425 

650 

850 

1000 


1.30 
1.65 
1.70 
1.75 


6.0 
7.0 
7.5 

8.0 


6 

12 

18 


70 
110 
145 


0.30 
0.23 
0.22 


1.30 
1.40 
1.60 


CONSTITUENTS   IN   100  POUNDS  OF  FEEDING  STUFFS 


FEEDING  STUFFS 


DRY  MATTER 
Pounds 


DIGESTIBLE 

PROTEIN 
OR  REPAIR 
MATERIAL 

Pounds 


NET  ENERGY 
Therms 


Coarse  Feeds 

Corn  silage 25.6 

Alfalfa  hay 91.6 

Clover  hay 84.7 

Corn  fodder 57.8 

Corn  stover 59.5 

Oat  hay . 84.0 

Timothy  hay 86.8 

Oat  straw 90.8 

Mangels 9.1 

Grains 

Barley 89.1 

Corn 89.1 

Corn  and  cob  meal  ....  84.9 

Oats 89.0 

Rye 88.4 

Wheat 89.5 

By-products 

Dried  brewers'  grains    .     .     .  92.0 

Cottonseed  meal  .     .     .     .     .  91.8 

Distillers'  grains 93.0 

Gluten  feed 91.9 

Gluten  meal 90.5 

Linseed  meal 90.8 

Malt  sprouts 89.8 

Dried  sugar-beet  pulp  .     .     .  93.6 

Wheat  bran 85.1 

Wheat  middlings       ....  84.0 


1.21 
6.93 
5.41 
2.13 
1.80 
2.59 
2.05 
1.09 
.14 


8.37 
6.79 
4.53 
8.36 
8.12 
8.90 


16.56 
34.41 
34.74 
30.53 
26.53 
36.97 
33.56 
21.21 
4.62 


80.75 
88.84 
72.05 
66.27 
81.72 
82.63 


19.04 
35.15 
21.93 
19.95 
33.09 
27.54 
12.36 
6.80 
10.21 
12.79 


60.01 
84.20 
79.23 
79.32 
78.49 
78.92 
46.33 
60.10 
48.23 
77.65 


340  APPLIED    CHEMISTRY 

EXERCISES 

Ex.  234.  What  is  meant  by  a  balanced  ration?  By  the  mainte- 
nance requirement  of  an  animal?  Do  large  animals  have  a  greater 
maintenance  requirement  than  small  ones?  Do  growing  animals  need 
proportionately  more  protein  in  their  foods  ?  Why  is  the  ash  of  the 
food  very  important  to  young  animals  ?  When  animals  are  doing  work, 
do  they  need  more  energy  producing  materials  than  when  not  working  ? 
Do  they  also  need  more  protein  ?  What  kind  of  foods  do  fattening  ani- 
mals need  —  those  high  in  protein  or  in  energy  ? 

Ex.  236.  How  much  protein  and  energy  are  needed  to  produce  a 
pound  of  milk?  Is  the  bulk  of  the  food  of  any  moment?  What  can 
you  say  about  the  effect  of  palatability  on  the  value  of  the  ration? 
How  important  is  it  to  study  the  individuality  of  the  animal  in  feeding  ? 

Ex.  236.     How  is  an  animal's  daily  ration  calculated  ? 

Ex.  237.  Calculate  a  ration  for  a  1000-pound  dairy  cow  that  gives 
30  pounds  of  milk  a  day.  Use  corn  fodder  and  alfalfa  hay  for  roughage 
and  any  of  the  foods  in  the  table  on  page  339  for  concentrates.  Cal- 
culate the  protein  and  the  energy  in  any  ration  used  on  your  home  farm 
and  note  whether  it  agrees  with  the  feeding  standards  given  in  this 
chapter. 

Ex.  238.  Calculate  the  ration  for  a  fattening  ox  weighing  1000 
pounds  according  to  the  Wolff-Lehman  tables  on  page  337,  using  corn 
stover  and  clover  hay  for  roughage.  Which  method  of  calculating  is  the 
simpler?  For  analyses  of  feeding  stuffs  see  Farmers'  Bulletin,  No.  22, 
U.  S.  Department  of  Agriculture,  or  any  of  the  larger  texts  on  feeding 
animals. 


CHAPTER  XLI 


HUMAN  FOODS 

384.  Food  Requirements  of  Human  Beings.  The  prin- 
ciples of  human  nutrition  are  exactly  the  same  as  those  for 
domestic  animals.  Men  and  women  need  protein  for  the  re- 
pair of  tissue  and  for  energy  to  enable  the  body  to  do  its  work, 
and  these  two  necessities  are  furnished  by  the  food,  just  as  in 
the  case  of  the  lower  animals.  The  food  requirements  of 
human  beings  are  indicated  by  dietary  standards  that  have 
been  worked  out  by  investigators.  The  following  standards 
of  daily  requirements  have  been  prepared  by  Atwater : 


CHARACTER  OP  WORK 

PROTEIN 

FAT 

CARBO- 
HYDRATES 

CALORIES 

Pounds 

Pounds 

Pounds 

Man  with  little  exercise     .     . 

0.20 

0.20 

0.66 

2450 

Man  with  light  work     .     .     . 
Man  with  moderate  work 

0.22 
0.28 

0.22 
0.28 

0.77 
0.99 

2800 
3520 

Man  with  hard  work     .     .     . 

0.39 

0.55 

1.43 

5700 

A  woman  is  supposed  to  require  eight  tenths  of  the  protein 
and  energy  needed  by  a  man ;  and  children  require  an  amount 
about  proportional  to  their  size  and  weight.  In  general 
terms  it  may  be  stated  that  according  to  this  standard  a 
man  of  average  size  and  doing  average  work  requires  about 
one  fourth  of  a  pound  each  of  protein  and  fat,  one  pound  of 

341 


342 


APPLIED   CHEMISTRY 


carbohydrates,  and  3200  calories  of  energy  daily.  Some 
writers  think  this  standard  too  high  and  hence  likely  to 
result  in  overfeeding. 

385.  Calculating  a  Balanced  Ration.  The  nutritive  value 
of  human  foods  varies  just  as  it  does  in  the  case  of  the  feeds 
for  the  farm  animals.  The  method  of  calculating  a  ration 
that  conforms  to  the  standard  is  exactly  the  same  as  that 
used  in  calculating  the  ration  for  cattle  or  horses  (382). 
The  following  combination  given  by  Snyder  serves  as  an 
example  of  a  day's  ration  which  would  meet  the  general 
standard  for  a  man  doing  average  work. 


FOODS 

AMOUNT  OF 
FOODS 
PER  DAY 

PROTEIN 

FAT 

CARBO- 
HYDRATES 

CALORIES 

Ounces 

Pounds 

Pounds 

Pounds 

Ham     

4 

0.04 

009 

480 

Eggs  (2)    .    .     .     . 

0.03 

0.02 

— 

136 

Bread 

8 

005 

001 

028 

650 

Butter  

2 

0.11 

r450 

Potatoes    .... 

12 

0.02 

0.14 

^285 

Milk 

16 

004 

004 

005 

325 

Suffar 

2 

0  12 

200 

Beef  stew 

4 

0.04 

0.05 

250 

Oatmeal    .... 

2 

0.02 

0.01 

0.09 

230 

Corn  meal      .     .     . 

4 

0.02 

0.01 

0.18 

420 

Totals     .     .     . 

0.26 

0.34 

0.86 

3426 

This  ration  contains  somewhat  less  carbohydrates  and 
more  fat  than  the  standard  and  furnishes  a  little  less  energy, 
but  it  is  close  enough  for  practical  purposes. 

386.  Practical  Use  of  Dietary  Standards.  It  is  neither 
practicable  nor  necessary  to  undertake  to  prepare  the  meals 
each  day  in  exact  conformity  to  a  dietary  standard.  An 


HUMAN  FOODS  343 

occasional  study  of  the  foods  served  in  the  family  to  ascertain 
how  closely  they  conform  to  the  standard  is  desirable,  be- 
cause such  a  study  gives  a  basis  for  modifying  the  diet,  if 
necessary  to  make  it  supply  the  proper  amount  of  protein 
and  energy.  It  is  practicable,  after  a  study  of  the  composi- 
tion of  the  different  foods,  to  make  combinations  that  will 
provide  in  a  general  way  the  right  proportions  of  protein  and 
energy,  and  to  avoid  combinations  that  are  too  high  in 
protein  or  that  carry  an  excess  of  energy.  In  other  words, 
it  is  practicable  to  avoid  a  combination  that  includes  several 
foods  high  in  protein,  or  one  made  up  of  several  foods  high  in 
energy  value  and  low  in  protein.  In  combining  foods  to 
form  balanced  rations  it  is  well  to  remember  that  lean  meats, 
fish,  dried  beans  and  peas,  oatmeal,  and  nuts  are  substances 
high  in  protein.  Fat  pork  products  and  other  fat  meats, 
cheese,  butter,  oils,  and  lard  supply  fats  in  large  proportions. 
Potatoes,  rice,  corn  meal,  cereals,  sugars,  cornstarch,  and 
tapioca  are  high  in  carbohydrates.  Wheat  flour  and  the 
other  foods  prepared  from  wheat  are  moderately  high  in  both 
protein  and  carbohydrates  and  low  in  fat. 

The  more  recent  studies  of  foods  indicate  that  the  subject 
is  much  more  complicated  than  was  formerly  supposed.  It 
is  not  sufficient  merely  to  balance  the  food  so  as  to  provide 
the  required  amount  of  protein,  fat,  carbohydrates,  and 
energy.  The  proteins  differ  among  themselves  in  character ; 
hence,  the  ration  should  contain  a  variety  of  proteins. 

It  has  been  discovered  also  that  most  common  foods  con- 
tain very  small  quantities  of  a  water-soluble  substance 
which  is  essential  for  the  maintenance  of  normal  body  con- 
ditions. This  substance  has  not  been  isolated  and  its  nature 
is  not  understood.  It  is  lacking  in  certain  prepared  foodstuffs 
such  as  polished  rice,  commercial  starch,  pure  sugar,  and  fats. 


344  APPLIED   CHEMISTRY 

Another  of  the  important  discoveries  of  modern  chemistry  is 
the  fact  that  there  is  a  fat-soluble  substance,  called  vitamine, 
which  seems  to  be  absolutely  necessary  to  growth  (Fig.  159). 
The  nature  of  this  substance  is  unknown,  but  it  is  known 
that  it  is  not  so  widely  distributed  as  is  the  water-soluble 
substance  mentioned  above.  It  is  found  in  milk,  especially 
in  the  milk  fat,  in  egg  yolk,  in  some  meats,  and  in  the  green 


A  B 

FIG.  159.  —  (A)  Rat  without  and  (5)  rat  with  fat-soluble  vitamines. 

leaves  of  plants.  It  is  not  found  in  seeds  except  in  the  germ, 
nor  in  oils  such  as  olive  and  cottonseed  oils.  A  lack  of  this 
fat-soluble  substance  in  the  food  prevents  the  growth  of 
young  animals  even  when  abundantly  supplied  with  food. 
The  fact  that  it  is  present  in  milk  is  one  of  the  reasons  why 
milk  is  so  valuable  a  part  of  the  diet  of  growing  children. 

There  is  a  difference  in  the  character  of  the  mineral  ele- 
ments, or  ash  constituents,  of  foods.  In  some  foods  the  acid- 
forming  elements  are  in  excess,  while  in  others  the  basic  or 
alkaline  elements  predominate.  Recent  investigations  in- 
dicate that  it  is  desirable  that  the  diet  should  contain  a 
slight  excess  of  basic  elements.  The  foods  that  furnish 
alkaline  mineral  substances  in  relatively  large  proportions 
are  tubers,  leafy  vegetables,  fruits,  and  milk.  The  cereals, 


HUMAN  FOODS  345 

meat,  fish,  and  eggs  contain  the  acid  mineral  elements  in 
excess.  It  would  seem,  therefore,  that  such  a  combination  as 
bread  and  milk  is  a  logical  one,  since  in  this  combination  the 
alkalinity  of  the  ash  materials  of  the  milk  overcomes  the 
acidity  of  the  cereal  ash. 

Palatability  is  even  more  important  in  human  foods  than 
in  animal  feeding  stuffs.  Food  should  be  so  prepared  as  to 
appeal  to  the  individual  by  its  appearance  and  flavor,  since 
pleasure  in  eating  undoubtedly  plays  a  part  in  insuring  a 
regular  and  normal  sequence  of  digestive  process. 

387.  Digestibility  of  Foods.  The  term  digestibility  has 
been  used  in  two  different  ways  by  physiologists  and  chem- 
ists :  (1)  to  designate  the  completeness  of  the  process  of  the 
digestion  of  the  food ;  and  (2)  to  designate  the  fact  that  the 
food  is  digested  without  causing  distress  or  discomfort  during 
the  process.  Some  confusion  has  arisen  from  this  double 
meaning.  Cheese,  for  example,  is  very  completely  digested ; 
but  since  it  is  commonly  considered  to  be  hard  to  digest, 
that  is,  to  cause  distress  after  eating,  it  is  often  said  to  be  indi- 
gestible. Bread,  which  is  digestible  according  to  the  second 
use  of  the  word,  is  not  so  completely  digested  as  cheese. 

Some  of  the  factors  affecting  the  digestibility  of  foods  are 
the  following :  (1)  Individuality  of  the  person.  Some  people 
can  easily  digest  foods  that  cause  great  discomfort  to  others. 
(2)  Mechanical  condition  of  food.  When  the  food  is  in  good 
mechanical  condition  it  is  more  easily  acted  upon  by  the 
digestive  juices.  (3)  The  combination  of  foods.  The  way  in 
which* foods  are  combined  is  of  importance,  as  some  foods 
seem  to  aid  in  the  digestion  of  others.  (4)  Method  of  prepara- 
tion. The  method  of  preparing  or  cooking  foods  exerts  an 
influence  on  their  digestibility.  Cooking  changes  both  the 
physical  and  the  chemical  condition  of  the  food,  and  influences 


346  APPLIED   CHEMISTRY 

the  ease  of  digestion  more  than  the  completeness  of  the 
process.  The  chief  advantages  of  cooking  are  probably 
the  development  of  a  more  pleasing  flavor,  and,  more  im- 
portant still,  the  complete  sterilization  of  food  that  may 
contain  injurious  bacteria  or  other  organisms. 

388.  Food  Adjuncts.     Spices,  such   as   allspice,  nutmeg, 
cinnamon,  and  ginger,  are  not  foods,  but  may  or  may  not  be 
useful  adjuncts  to  the  diet.     They  stimulate  the  appetite 
and  promote  secretion  of  the  gastric  juice,  which  may  be 
beneficial  or  may  induce  overeating.     Such  substances  are 
called  condiments.     Vinegar  is  a  condiment  and  is  used 
largely  because  of  the  pleasant  acidity  of  its  acetic  acid. 

Coffee  or  tea  have  little  or  no  nutritive  value  but  are  used 
because  of  the  stimulating  effect  of  the  alkaloid  caffein 
which  they  contain.  Cocoa  contains  a  similar  alkaloid  but 
has  some  nutritive  value  as  well,  because  of  its  fat  content. 

389.  Fresh  Fruits.     Considered  strictly  from  the  chemical 
standpoint,  fruits  seem  to  have  little  food  value,  as  they  are 
low  in  both  protein  and  energy.     Fresh  fruits  contain  from 
85  to  95  per  cent  water,  a  fraction  of  1  per  cent  of  fat  and 
protein,  and  only  5  to  10  per  cent  of  carbohydrates.     They 
contain,  however,  acids,  organic  salts,  and  other  substances 
which  are  believed  to  have  a  beneficial  effect  on  the  system, 
and  they  doubtless  often  stimulate  the  appetite  for  other 
food.     Fruits  also  add  to  the  attractiveness  of  the  diet,  and 
the  appearance  of  the  food  is  a  matter  of  considerable  im- 
portance.    The  ash  of  fruits  is  rich  in  potassium,  calcium, 
and  iron  salts,  all  of  which  are  valuable  to  the  body.   -Dried 
fruits,  such  as  dates,  raisins,  and  figs,  are  foods  in  the  more 
restricted  sense,  as  they  furnish  a  large  amount  of  digestible 
nutrients.     Dates,  especially,  form  a  large  part  of  the  diet 
of  certain  Oriental  people. 


HUMAN  FOODS  347 

390.  Dietary  Studies.     A  dietary  study  takes  into  con- 
sideration the  cost  and  amount  of  nutrients  consumed  by 
individuals  or  families.     It  is  an  investigation  in  which  men 
and  women  and  human  foods  are  used  instead  of  farm  an- 
imals and  animal  feeds.     In  a  dietary  study,  the  amounts  of 
nutrients  in  the  edible  portion  of  the  foods  are  determined  by 
chemical  analysis  or  calculated  from  the  tables  of  composition. 
These  studies  take  into  consideration  the  cost  of  the  material 
as  well  as  the  amounts  of  protein  and  energy  used  by  each 
person  or  group.     Such  studies  show  that  lack  of  knowledge 
in  regard  to  the  values  of  foods  has  frequently  resulted  in 
whole  families  being  underfed,  not  from  necessity,  but  from 
lack  of  judgment  in  the  selection  of  foods.     It  too  often 
happens  that  choice  of  foods  is  made  wholly  on  the  basis  of 
palatability,  instead  of  on  the  cost  of  the  nutrients  and  the 
kind  of  work  to  be  performed.     Dietary  studies  show  that 
for  long  periods  the  best  results  are  obtained  when  the  foods 
are  combined  in  such  a  way  as  to  furnish  the  different 
nutrients  in  approximately  the  amounts  given  in  the  dietary 
standards.     By  studying  the  diet  it  is  often  possible  to  re- 
duce the  cost  of  the  food  without  impairing  its  nutritive 
value  if  indeed  the  nutritive  value  is  not  actually  increased. 

391.  Food  Fads.     Much  of  the  matter  that  has  been 
written  on  the  subject  of  foods  is  wholly  without  scientific 
basis,  even  when  it  pretends  to  be  scientifically  presented. 
Vegetarianism,  or  the  exclusive  use  of  vegetable  foods,  is 
advocated  by  some  people ;  but  there  is  no  scientific  evidence 
that  mankind  is  benefited  by  an  exclusively  vegetable  diet. 
The  long-continued  experience  of  the  human  family  on  a 
mixed  diet  of  cooked  meats  and  vegetables  is  evidence  that 
such  a  diet  is  healthful,  and  there  are  many  indications  that 
the  best  diet  is  one  that  contains  a  reasonable  amount  of 


348  APPLIED   CHEMISTRY 

animal  protein.  Many  so-called  vegetarians  obtain  this 
animal  protein  through  the  use  of  milk  and  eggs;  but  of 
course  in  such  conditions  the  diet  is  no  longer  strictly  vege- 
tarian. It  is  probably  true  that  American  families  use  more 
animal  protein  than  is  necessary,  a  practice  which,  while  it  may 
not  be  injurious,  results  in  an  unnecessarily  expensive  diet. 

The  exclusive  use  of  raw  foods  is  another  food  fad  that  has 
no  scientific  basis,  and  it  is  not  surprising  that  the  cult  has  a 
comparatively  small  following.  Unfortunately  a  large  part 
of  the  literature  on  foods  has  been  written  by  dyspeptics  or 
by  people  who  have  prepared  foods  of  some  kind  to  sell. 

392.  What  to  Eat.  Probably  the  only  advice  that  can 
safely  be  given  is  about  as  follows :  (1)  make  the  diet  agree 
approximately  with  the  ratios  between  protein,  fat,  and 
carbohydrates  as  given  in  the  dietary  standard ;  (2)  provide 
a  part  of  the  protein  from  animal  sources;  (3)  consume 
moderate  amounts  of  such  a  balanced  food;  (4)  avoid  all 
foods  that  personal  experience  has  shown  to  produce  dis- 
comfort; (5)  have  as  much  variety  as  possible  in  the  diet, 
including  the  use  of  green  and  succulent  vegetables ;  (6)  com- 
bine coarse  or  laxative  foods  with  those  that  are  more 
completely  digested;  (7)  use  fresh  fruits  abundantly,  if 
possible;  (8)  use  condiments  or  the  stimulating  beverages 
such  as  tea  and  coffee  only  moderately ;  (9)  remember  that 
the  highest  priced  foods  are  often  the  least  nutritious,  and 
that  there  is  no  close  relation  between  cost  and  food  value ; 
(10)  use  only  foods  that  have  been  carefully  protected  from 
bacterial  contamination. 

Millions  of  dollars  have  been  spent  by  manufacturers  in  the 
last  few  years  in  advertising  the  many  brands  of  breakfast 
foods  on  the  market.  In  general,  it  may  be  said  that  these 
breakfast  cereals  have  no  greater  nutritive  value  than  the 


HUMAN  FOODS  349 

grains  from  which  they  were  prepared.  Breakfast  cereals 
made  from  corn  are  equal  to  the  same  weight  of  corn  meal, 
for  example,  and  those  made  from  wheat  are  no  more  valu- 
able than  the  wheat  itself.  The  price  paid  for  each  pound 
of  actual  nutrients  in  the  breakfast  foods  is  several  times 
the  cost  of  the  same  nutrients  in  corn  meal  or  wheat  flour. 

EXERCISES 

Ex.  239.  What  is  meant  by  a  dietary  standard?  What  is  the 
approximate  dietary  requirement  of  a  man  doing  average  work? 
How  should  you  calculate  a  balanced  ration  for  a  man  ?  What  practical 
daily  use  can  be  made  of  dietary  standards?  Name  some  foods  high 
in  protein ;  some  high  in  fats ;  some  high  in  carbohydrates. 

Ex.  240.  Make  a  list  of  the  foods  used  on  your  home  table  for 
each  meal  for  a  day.  Does  the  combination  appear  to  be  too  high  in 
protein  ?  In  energy  materials  ?  Would  a  little  change  improve  it  ?  For 
the  composition  of  the  common  foods,  see  Farmers'  Bulletin  142,  or 
Office  of  Experiment  Station  Bulletin  28,  U.  S.  Department  of  Agricul- 
ture. 

Ex.  241.  In  what  two  ways  is  the  term  digestibility  used  ?  What 
are  some  of  the  factors  which  affect  digestibility  of  foods  ?  Tell  what 
you  can  about  the  food  value  of  fruits. 

Ex.  242.  Of  what  value  is  a  dietary  study  ?  How  is  it  conducted  ? 
What  do  these  studies  sometimes  show?  Study  some  of  the  bulletins 
of  the  United  States  Department  of  Agriculture  on  dietary  studies. 

Ex.  243.  State  ten  practical  points  to  be  observed  in  deciding 
what  to  eat.  What  can  you  say  about  food  fads  ?  What  can  you  say 
about  the  value  of  the  prepared  breakfast  foods  ? 


CHAPTER  XLII 
MILK  AND   ITS  PRODUCTS 

393.  Secretion  of  Milk.     Milk  is  a  fluid   secreted  by 
the  mammary  glands  of  all  animals  that  suckle  their  young. 
It  contains  in  a  palatable  and  easily  digested  form  all  the 
nutrients    necessary    for    the    nourishment    of  the  young 
animal.     Market  milk  in  this  country  is  almost  entirely 
cow's  milk,  but  the  goat  and  the  water  buffalo  are  important 
sources  of  milk  supply  in  some  other  countries.     In  the  wild 
state  the  cow  produced  only  sufficient  milk  to  nourish  the 
calf  until  it  could  subsist  upon  other  food,  but  under  domesti- 
cation the  secretion  of  milk  by  the  cow  has  been  greatly 
increased  by  careful  selection  and  liberal  feeding. 

394.  Composition  of  Milk.     The  essential  constituents  of 
milk  are  water,  fat,  protein,  sugar,  and  ash  or  mineral  salts. 
The  average  composition  of  cow's  milk  is  shown  in  the  follow- 
ing table : 

AVERAGE  COMPOSITION  OF  Cow's  MILK  IN  PER  CENTS 

f  Water    87.2 
Cow's  milk    100 1 

Solids 


12.8 

Fat.     . 
Protein 
Sugar  . 
Ash. 

.    3.75  („      . 
32      Casein    . 

_'      [Albumin 

o      O.lO 

0.7 

.    2.5 
.    0.7 

There  is  considerable  variation  in  the  composition  of  the 
milk  from  different  cows.  The  most  variable  constituent  of 
the  milk  is  its  fat  content.  Some  cows  produce  milk  with  as 

850 


MILK  AND  ITS  PRODUCTS  351 

little  as  2  per  cent  of  fat,  while  other  cows  have  been  known 
to  produce  milk  containing  as  much  as  8  or  9  per  cent  of  fat. 
The  other  constituents  of  the  milk  are  fairly  constant  in 
amount  even  in  milks  that  vary  greatly  in  fat  content. 
The  quantity  and  the  quality  of  the  milk  produced  by  a  cow 
depend  upon  a  number  of  factors.  Certain  breeds,  such  as 
the  Jersey  and  Guernsey,  as  a  rule  produce  a  relatively  small 
quantity  of  milk,  which  is  high  in  fat ;  while  the  Holstein  and 
Ayrshire  breeds  give  larger  quantities  of  milk,  which  is  low  in 
the  percentage  of  fat.  Individual  animals  within  any  of 
these  breeds  differ  in  the  quantity  and  the  quality  of  the  milk 
they  produce.  The  kind  and  the  amount  of  feeds  the  animal 
receives  have  an  influence  on  the  amount  of  milk  produced, 
but  apparently  have  no  effect  upon  the  quality  of  the  milk. 
The  richness  of  a  cow's  milk  seems  to  be  natural  to  her  and  is 
not  affected  by  the  feeds  she  eats,  although  the  quantity  of 
milk  she  produces  may  be  so  affected.  A  cow  usually  pro- 
duces the  most  milk  per  day  within  a  month  after  the  calf  is 
born,  and  the  amount  gradually  decreases  until  the  secretion 
ceases  as  the  cow  goes  dry.  As  the  amount  of  milk  decreases, 
the  percentage  of  fat  is  slightly  increased.  The  first  milk 
drawn  from  the  udder  at  any  milking  is  much  poorer  in 
quality  than  the  last.  The  first  often  tests  as  low  as  1  per 
cent  of  fat  and  the  last  as  high  as  8  or  9  per  cent  fat. 

395.  Fat  of  Milk.  This  fat  occurs  in  the  form  of  small 
globules  (Fig.  160)  which  can  be  seen  only  under  the  mi- 
croscope. The  globules  average  about  one  six-thousandth 
of  an  inch  in  diameter.  The  size  of  the  globule  averages 
larger  in  the  milk  of  Jerseys  and  Guernseys  than  in  that  of 
Ayrshires  or  Holsteins.  Any  sample  of  milk,  however,  con- 
tains globules  that  vary  greatly  in  size.  The  fat  globules 
are  held  in  suspension  by  the  other  solids  of  the  milk  in  the 


352 


APPLIED   CHEMISTRY 


form  of  an  emulsion.  The  fat  of  milk  is  commonly  called 
butter  fat.  It  differs  chemically  from  other  fats  in  that  it 
contains  about  5  per  cent  of  butyrin,  the  glycerin  salt  of 
butyric  acid,  H-  C4H7O2  (299).  The  fat  has  a  much  higher 


FlG.  160.  —  Appearance  of  milk  under  the  microscope,  showing  groups  of  fat 
globules.     In  the  circle  the  fat  globules  are  more  highly  magnified. 

commercial  value  than  any  other  part  of  the  milk,  and  con- 
sequently the  price  of  milk  is  usually  based  on  its  fat  content. 
396.  Casein.  The  principal  protein  of  milk  is  casein  and  it 
gives  skim  milk  its  bluish-white  color.  When  acid  is  added  to 
milk  the  casein  separates  in  the  form  of  a  curd.  The  natural 
curdling  of  milk  is  caused  by  the  lactic  acid  formed  in  the 
milk  when  it  sours  (290).  The  casein  can  also  be  separated 
from  the  milk  by  means  of  rennet,  which  is  a  preparation 
made  from  the  stomachs  of  very  young  calves  and  contains 
the  enzyme  rennin  (358).  When  this  material  is  added  to 
milk,  the  casein  separates  in  the  form  of  a  sweet  curd,  which 
firmly  incloses  nearly  all  the  fat  that  the  milk  contains. 
This  curd  forms  the  starting  point  in  the  manufacture  of 
cheese.  Junket  tablets  contain  dried  rennet.  In  making 
junket  just  enough  rennet  is  used  to  coagulate  the  casein 


MILK  AND  ITS  PRODUCTS  353 

and  change  the  milk  into  a  jelly  like  mass  without  causing 
the  casein  to  separate. 

397.  Albumin  of  Milk.    This  is  much  like  the  white  of  egg. 
Like  all  albumins  it  is  soluble  in  water,  and  as  it  is  not  pre- 
cipitated by  acid  it  remains  in  solution  when  the  casein  is 
separated  either  by  acid  or  rennet.     Boiling  the  clear  liquid, 
or  whey,  which  remains  after  the  casein  is  removed  coagulates 
the  albumin  and  causes  it  to  separate  in  white  flakes.     The 
tough  scum  which  forms  on  the  surface  of  milk  when  it  is 
boiled  is  composed  largely  of  coagulated  albumin. 

398.  Sugar  of   Milk.       Lactose   or  milk  sugar  has    the 
formula  C^I^On  (310).      This  sugar  occurs  only  in  milk. 
In  commerce  it  is  found  as  a  fine  white  powder  with  a  mild, 
sweet  taste.      It  is  about  one  sixth  as  sweet  as  cane  sugar. 
It  is  readily  acted  upon  by  the  bacteria  in  the  milk  and  is 
changed  into  lactic  acid : 

Ci2H22On  +  H2O  •>•  4  H-  C3H5O3 

lactic  acid. 

It  is  this  acid  that  makes  milk  sour  and  causes  the  casein  to 
curdle  or  separate.  When  about  0.4  per  cent  of  lactic  acid  is 
present  the  milk  acquires  a  sour  taste,  and  when  the  amount 
reaches  0.6  to  0.7  per  cent  it  begins  to  curdle.  Ordinarily 
the  acid  will  not  develop  beyond  0.9  per  cent. 

399.  Ash  of  Milk.     The  mineral  matter  left  after  burning 
off  the  organic  matter  is  the  ash  of  milk.      It  contains  all 
the  compounds  necessary  to  build  the  bony  structure  of  the 
growing  animal.     The  most  important  elements  in  the  ash  are 
calcium,  phosphorus,  iron,  potassium,  magnesium,  and  sul- 
phur.    The  mineral  matter  is  probably  largely  combined 
with  the  casein  and  albumin  in  the  milk. 

400.  Milk  and  Bacteria.     Since  milk  is  a  complete  food 
and  is  in  a  liquid  form,  it  is  an  ideal  medium  for  the  growth 

EV.  CHEM. — 23 


354 


APPLIED   CHEMISTRY 


FIG.  161.  —  Showing  the  rapid  development 
of  bacteria  in  milk,  a,  a  single  bacterium  ; 
6,  increase  in  24  hours  when  properly 
cooled ;  c,  increase  when  not  cooled. 


of  bacteria,  molds,  and  other  organisms.  Bacteria,  es- 
pecially those  which  cause  the  souring  of  milk,  are  so  widely 
distributed  that  it  is  difficult  to  keep  them  out  of  milk,  and 

for  this  reason  the  pro- 
duction of  milk  which  is 
pure  enough  for  human 
consumption  requires 
more  care  than  any  other 
work  on  the  farm .  Care- 
ful attention  should  be 
given  to  the  surround- 
ings, to  the  cleanliness 
of  the  cow,  to  the  actual 
process  of  milking,  and  to  the  utensils  used,  so  as  to  prevent 
as  far  as  possible  the  introduction  of  bacteria  into  the  milk. 
Disease-producing  germs  should  be  especially  guarded 
against,  as  many  of  them  grow  rapidly  in  milk.  Diseases 
have  often  been  spread 
in  this  way. 

It  is  practically  im- 
possible to  keep  all  acid- 
forming  bacteria  out  of 
the  milk ;  but  if  the  milk 
is  cooled  immediately 
upon  being  taken  from 
the  cow,  their  growth 
will  be  retarded  and 
the  milk  will  keep  sweet 
longer  than  when  this  precaution  is  not  taken  (Fig.  161). 

Milk  that  has  been  boiled  to  kill  the  bacteria  is  said  to  be 
sterilized.  Such  milk  if  carefully  stored  will  keep  a  com- 
paratively long  time  but  has  a  cooked  taste.  Sometimes  the 


FIG.  162.  —  Pasteurizing  apparatus. 


MILK  AND  ITS  PRODUCTS  355 

milk  is  heated  to  145°  F.  for  from  20  to  40  minutes  and  is 
then  rapidly  cooled,  when  it  is  said  to  be  pasteurized  (Fig. 
162).  Such  milk  does  not  have  the  taste  of  boiled  milk 
and  if  stored  in  a  cool  place  will  keep  sweet  for  a  few  days. 
This  process  kills  most  of  the  active  bacteria  and  thus  delays 
the  souring. 

Antiseptic  materials,  such  as  boric  acid,  salicylic  acid,  and 
formalin  are  sometimes  added  to  milk  to  preserve  it ;  but  this 
practice  is  illegal.  Any  antiseptic  that  will  prevent  the  growth 
of  bacteria  is  unfit  for  use  in  any  food  intended  for  human 
consumption.  Such  materials  are  especially  harmful  in 
milk  to  be  used  for  infant  feeding. 

401.  Cream  and  Skim  Milk.  The  fat  of  milk  is  lighter 
than  the  liquid  portion  of  the  milk.  The  specific  gravity  of 
the  fat  is  about  0.9,  while  the  rest  of  the  milk  has  a  specific 
gravity  of  about  1.036.  The  fat  globules  being  lighter  tend 
to  rise  to  the  surface,  where  they  form  a  layer  known  as 
cream.  The  larger  the  globule  the  more  rapidly  it  rises ;  so 
the  milk  of  the  Jersey  and  Guernsey  breeds  creams  more 
easily  than  that  from  the  breeds  with  smaller  fat  globules, 
such  as  the  Ayrshire  and  Holstein.  The  smaller  the  fat 
globule,  the  larger  is  its  surface  in  proportion  to  its  volume, 
and,  consequently,  the  greater  the  resistance  to  its  rise. 
Cream  may  contain  from  12  to  50  per  cent  of  fat.  That  part 
of  the  milk  that  remains  when  the  cream  ;s  removed  is  known 
as  skim  milk.  It  differs  from  whole  milk  in  containing  only 
0.1  to  0.4  per  cent  of  fat.  When  milk  is  allowed  to  stand  in 
deep  or  shallow  pans  until  the  cream  collects  on  the  surface 
(24  to  36  hours),  the  cream  is  said  to  have  been  separated  by 
gravity.  Milk  held  in  deep  cans  which  are  allowed  to  stand 
in  cold  water  creams  more  completely  than  when  set  in 
shallow  pans. 


356  APPLIED   CHEMISTRY 

402.  Cream  Separators.  At  the  present  time  most  of 
the  cream  is  produced  by  skimming  the  milk  by  the  cen- 
trifugal cream  separator.  In  this  machine  centrifugal  force 
generated  by  a  rapidly  revolving  bowl  takes  the  place  of 
gravity  and  acts  with  a  much  greater  force.  As  the  milk 
flows  into  the  revolving  bowl  in  a  continuous  stream,  it  is 
acted  upon  by  centrifugal  force  and  flies  to  the  outer  wall 
of  the  bowl.  The  skim  milk  being  heavier  than  the  cream 
is  forced  out  and  against  the  side  of  the  bowl,  forcing 
the  cream  toward  the  center.  By  providing  suitable  out- 
lets the  skim  milk  can  be  directed  into  one  channel  and 
the  cream  into  another.  The  skimming  is  more  complete 
if  the  milk  is  first  warmed  to  about  85°  F.  If  separated 
as  soon  as  it  is  milked  the  temperature  is  right  without 
artificial  heating. 

The  skimming  by  the  separator  is  much  more  complete 
than  by  any  of  the  gravity  methods.  A  properly  working 
separator  will  leave  not  to  exceed  0.1  per  cent  of  fat  in  the 
skim  milk,  while  gravity  creaming  may  leave  from  0.4  to  0.8 
per  cent.  The  average  per  cent  composition  of  separator 
skim  milk  is  about  as  follows : 

Water 90.54 

Fat 0.10 

Sugar 4.94 

Proteins 3.53 

Ash 0.89 

Skim  milk  contains  all  the  materials  found  in  whole 
milk  with  the  exception  of  fat.  It  has  a  high  food  value, 
and  its  use  as  a  human  food  deserves  more  consideration  than 
it  has  received  in  this  country.  Its  value  as  a  food  for  farm 
animals  has  long  been  recognized. 

The  use  of  the  separator  has  the  added  advantage  that  the 


MILK  AND   ITS  PRODUCTS 


357 


skimming  is  done  while  the  milk  is  fresh  and  sweet  and  that 
therefore  both  the  cream  and  the  milk  are  in  the  best  con- 
dition for  use  as  foods.  Separators  vary  in  capacity  from  the 
small  hand  machines  that  will  handle  150  pounds  of  milk  an 
hour  to  power  machines  with  a  capacity  of  4000  pounds  or 
more  an  hour. 

403.  Butter.  When  cream  is  agitated  for  some  time  at 
the  right  temperature,  the  fat  globules  unite  into  larger  and 
larger  aggregates, 
and  the  fat  finally 
separates  in  irregular 
masses  of  butter. 
The  process  of  agi- 
tating the  cream  is 
known  as  churning. 
Many  different  kinds 
of  churns  are  in  use, 
the  types  varying 
from  the  old-fash- 
ioned dasher  churn  to 
the  more  modern 
barrel-shaped  churns. 

The  proper  tem- 
perature for  churning 
ranges  from  50  to  58 

degrees  F.,  varying  with  different  samples  of  cream.  Churn- 
ing should  cease  when  the  granules  of  butter  are  the  size  of 
wheat  grains.  The  butter  is  then  washed  with  cold  water  to 
remove  the  buttermilk,  and  is  finally  worked  to  remove 
excess  of  water.  During  the  working  salt  is  added  gradually, 
although  a  few  American  and  many  European  markets  demand 
unsalted  butter.  American  butter  contains  on  the  average 


FIG.  163.  —  Churning  butter  in  Palestine. 


358  APPLIED   CHEMISTRY 

from  83  to  85  per  cent  of  fat,  12  to  15  per  cent  of  water,  and 
from  2  to  4  per  cent  of  salt. 

404.  Ripening  of  Cream.     Butter  made  from  perfectly 
sweet  cream  is  considered  by  many  to  have  an  insipid  taste. 
In  order  to  develop  the  flavor  preferred  by  the  general  market 
and  to  facilitate  the  churning,  the  cream  is  allowed  to  become 
slightly  acid  before  it  is  churned.     This  is  known  as  the 
ripening  of  the  cream.     The  cream  is  properly  ripened  when 
it  contains  about  one  half  per  cent  of  lactic  acid.     Since 
many  of  the  bacteria  that  find  their  way  into  milk  produce 
undesirable  flavors  in  the  cream,  in  order  to  insure  the  proper 
fermentation  it  is  customary  to  add  a  pure  culture  of  the 
desired  bacteria,  known  as  a  starter.     In  many  creameries 
the  cream  is  first  pasteurized  to  kill  most  of  the  native  bac- 
teria, and  the  starter  is  then  added.     This  method  makes  it 
much  easier  to  control  the  flavor  of  the  butter. 

405.  Buttermilk  is  the  liquid  remaining  in  the  churn  after 
the  separation  of  the  butter  from  the  cream.     It  contains 
about  90  per  cent  water,  3.5  percent  proteins, 0.5  per  cent  fat, 
4.0  per  cent  sugar,  and  0.5  per  cent  lactic  acid.     The  finely 
divided  condition  of  its  proteins  makes  it  readily  digested. 
The  mildly  acid  taste  of  buttermilk  is  pleasing  to  some 
people  and  very  distasteful  to  others.     Buttermilk  is  growing 
in  popularity  as  a  food  and  a  beverage  to  such  an  extent 
that  many  factories  are  now  producing  large  quantities  of 
artificial  buttermilk.     This  is  made  by  adding  a  starter 
to  skim  milk  and  allowing  the  proper  degree  of  acidity  to 
develop ;  when  this  acidity  is  properly  developed,  the  milk 
is  churned  to  break   the   curd   into   fine  particles  such  as 
exist  in  natural  buttermilk.     If,  as  is  sometimes  done,  a 
little  cream  is  added,  the  product  is  known  as  creamed 
buttermilk. 


MILK  AND   ITS  PRODUCTS  359 

406.  Condensed  Milk  and  Milk  Powders.     Condensed 
milk  is  prepared  by  evaporating  the  water  from  milk  in  a 
vacuum  pan  until  the  milk  is  reduced  to  about  one  third  or 
one  fourth   of   the   original   volume.     The   evaporation   is 
carried  on  under  reduced  pressure  so  that  the  milk  need  not 
be  heated  to  a  sufficiently  high  temperature  to  impart  to  it  a 
cooked  flavor.     The  condensed  milk  is  then  sealed  in  cans 
and  sterilized  by  exposing  the  can  to  superheated  steam.     In 
some  brands  of  condensed  milk  the  sterilization  is  omitted, 
and  about  40  per  cent  of  cane  sugar  is  added  to  prevent 
fermentation.      The  unsweetened  condensed  milk  is  quite 
commonly  called  evaporated  milk  or  evaporated  cream  to  dis- 
tinguish it  from  the  sweetened  condensed  milk. 

Milk  powders  are  prepared  by  evaporating  the  milk  to 
complete  dryness.  A  good  sample  of  milk  powder  is  as  fine 
as  flour,  and  when  stirred  up  with  water  makes  a  mixture 
having  the  properties  of  milk.  Most  of  the  milk  powders 
are  made  from  skimmed  or  partially  skimmed  milk.  It 
is  said  that  milk  powder  prepared  from  whole  milk  will 
not  keep  on  account  of  the  large  amount  of  fat  that  it 
contains. 

407.  Cheese.     A  great  number  of  varieties  of  cheese  are 
found  in  the  market,  most  of  which  are  prepared  by  the 
action  of  rennin  (358)  on  milk.    The  variety  most  largely 
used  in  this  country  belongs  to  the  type-  known  as  Cheddar 
cheese  and  is  commonly  known  as  American  cheese. 

In  making  American  Cheddar  cheese,  after  the  milk  has 
been  allowed  to  develop  about  0.25  per  cent  of  lactic  acid  a 
small  quantity  of  rennet  extract  is  added,  and  the  milk  is  kept 
at  a  temperature  of  about  85  degrees  F.  In  about  thirty 
minutes  the  milk  sets  into  a  firm,  jellylike  curd.  This  curd 
is  then  cut  into  small  cubes  with  specially  devised  knives,  and 


360  APPLIED   CHEMISTRY 

the  temperature  of  the  vat  is  raised  to  100°  F.  At  this 
temperature  the  curd  shrinks  quite  rapidly  and  more  acid 
develops  and  is  absorbed  by  the  curd.  After  one  or  two 
hours  the  whey  is  drawn  from  the  vat  and  the  curd  mats  into 
a  solid  mass.  After  some  time  it  is  passed  through  a  mill  to 
shred  it  and  is  then  salted  and  pressed  into  molds.  The 
cheese  is  then  placed  in  the  curing  room  for  a  period  in  order 
to  ripen  and  develop  flavor. 

When  the  cheese  is  first  made,  it  is  tasteless  and  very 
tough  and  rubbery,  and  is  not  readily  digested.  After  a 
period  of  ripening  the  cheese  becomes  soft  and  plastic  and 
develops  a  flavor  which  increases  in  intensity  with  the  age  of 
the  cheese.  Practically  none  of  the  nitrogenous  compounds 
of  the  new  cheese  are  soluble  in  water,  while  in  old  cheese  over 
half  of  these  compounds  are  soluble.  In  other  words  the 
cheese  has  been  partially  digested  during  the  ripening  process. 
A  good  American  cheese  contains  about  26  per  cent  of  pro- 
teins and  33  per  cent  of  fat. 

Very  slight  differences  in  the  amount  of  rennet  added,  in 
the  temperature  at  which  the  milk  is  set,  in  the  amount  of 
acid  developed,  or  in  the  temperature  and  moisture  of  the 
curing  room  produce  marked  differences  in  the  appearance 
and  flavor  of  the  cheese ;  consequently  there  are  almost  end- 
less varieties  of  cheeses  on  the  market,  varying  from  the  very 
soft  Brie  and  Camembert  to  the  firm  Cheddar  and  Swiss 
cheeses.  In  some  varieties,  such  as  Roquefort,  molds  are 
added  to  produce  a  special  flavor.  Goat's  milk  and  sheep's 
milk  are  also  sometimes  used  in  cheese  making. 

The  whey  left  in  cheese  making  contains  most  of  the  albu- 
min and  the  sugar  originally  present  in  the  milk.  The 
albumin  is  sometimes  coagulated  by  heat  and  used  to  make 
an  albumin  cheese.  In  some  factories  the  sugar  is  recovered 


MILK  AND   ITS  PRODUCTS  361 

by  evaporation  and  is  sold  under  the  name  of  lactose,  or 
milk  sugar,  for  use  in  medicine. 

Cottage  cheese,  or  pot  cheese,  is  made  from  the  curd  of 
sour  milk  without  the  use  of  rennet.  The  curd  is  firmed  by 
heat  and  the  whey  drained  off  through  a  cloth  strainer.  Salt 
is  added  and  the  product  is  improved  by  the  addition  of 
cream,  and  sometimes  by  the  use  of  nutmeg,  caraway,  or 
other  spices.  A  similar  cheese  is  made  from  buttermilk. 

408.  Other  Milk  Products.  In  some  creameries  the  skim 
milk  is  utilized  for  the  production  of  dried  casein.  Sul- 
phuric acid  is  used  to  curdle  the  milk  and  the  casein  is  pressed 
and  then  dried.  The  casein  thus  prepared  is  used  as  a  sizing 
for  paper  and  in  the  manufacture  of  certain  cements.  It  is 
used  also  in  massage  creams  and  in  some  cosmetics.  Casein 
so  treated  as  to  make  it  very  hard  is  used  in  making  billiard 
balls  and  knife  handles  under  the  name  of  artificial  ivory. 

Koumiss  is  a  beverage  made  from  milk.  Yeast  and  sugar 
are  added  to  the  milk,  and  the  ensuing  fermentation  results 
in  the  production  of  a  small  percentage  of  alcohol.  Koumiss 
was  originally  made  in  Russia  from  mare's  milk. 

Bulgaris  milk  is  usually  made  from  skim  milk  by  the  action 
of  a  species  of  bacteria,  known  as  Bacillus  bulgaricus. 
These  bacteria  cause  the  milk  to  become  sour  without  the 
separation  of  the  casein.  Bulgaris  milk  tastes  very  much  like 
buttermilk,  but  often  has  a  higher  acidity. 

EXERCISES 

Ex.  244.  What  are  the  constituents  of  milk?  What  constituent 
is  most  variable  in  the  amount  present?  How  does  the  breed  affect 
the  amount  of  fat  in  the  milk?  Does  the  feed  change  the  percentage 
of  fat  in  a  cow's  milk  ?  Can  the  quantity  of  milk  be  changed  by  vary- 
ing the  feed?  Which  contains  the  most  fat  —  that  first  drawn  from  the 
udder  or  the  strippings  ? 


362  APPLIED   CHEMISTRY 

Ex.  245.  Examine  a  drop  of  milk  under  the  microscope.  In  what 
form  is  the  fat  present  in  the  milk  ?  How  large  are  these  globules  ? 
What  eff ect  does  the  breed  of  cow  have  on  the  size  of  the  globule  ?  What 
is  the  characteristic  compound  of  butter  fat?  Why  does  the  per- 
centage of  fat  usually  determine  the  value  of  the  milk  ? 

Ex.  246.  To  some  skim  milk  add  a  little  vinegar  or  acetic  acid. 
What  is  the  curd  which  forms  ?  To  another  portion  of  the  milk  add  a 
little  rennet  extract  or  a  little  pepsin.  What  happens?  How  much 
casein  does  ordinary  milk  contain  ? 

Ex.  247.  Pour  off  the  clear  liquid  from  the  milk  to  which  the  vine- 
gar was  added  in  the  last  exercise  and  heat  nearly  to  boiling.  Does 
albumin  separate  ?  How  does  albumin  compare  with  the  white  of  egg  ? 

Ex.  248.  (Teacher)  To  a  quart  of  skim  milk  add  just  enough  acid 
to  coagulate  the  casein.  Heat  the  whey  to  coagulate  the  albumin. 
Skim  off  the  albumin  and  evaporate  the  liquid  to  dryness  to  obtain 
milk  sugar.  What  are  the  properties  of  milk  sugar  ?  What  change 
takes  place  when  the  milk  sours  ?  How  much  lactic  acid  must  develop 
in  the  milk  before  it  curdles  ? 

Ex.  249.  What  mineral  elements  are  found  in  milk  ?  Of  what  use 
are  they  to  the  young  animal  ?  To  obtain  the  ash  from  milk  place  the 
milk  in  an  evaporating  dish,  add  sufficient  nitric  acid  to  coagulate  the 
casein,  evaporate  to  dryness,  and  burn  off  the  organic  matter. 

Ex.  260.  Why  do  bacteria  grow  so  readily  in  milk?  How  do  the 
bacteria  get  into  the  milk  ?  What  precautions  are  necessary  to  produce 
clean  milk  ?  How  does  immediate  cooling  of  the  milk  affect  its  keeping 
quality?  What  is  meant  by  sterilized  milk?  By  pasteurized  milk? 
Why  do  they  keep  longer  than  ordinary  milk  ?  Why  should  all  antisep- 
tic materials  be  avoided  in  milk  ?  Test  a  sample  of  milk  for  formalde- 
hyde as  follows  :  place  a  little  milk  in  a  test  tube ;  incline  the  tube  and 
pour  a  little  sulphuric  acid  such  as  is  used  in  the  Babcock  test  down  the 
side  of  the  tube  so  that  it  will  underlie  the  milk.  If  formaldehyde  is 
present,  a  purple  ring  will  appear  at  the  junction  of  the  milk  and  acid. 

Ex.  251.  When  milk  stands  why  does  the  cream  form  at  the  top? 
How  much  fat  does  cream  contain  ?  What  is  skim  milk  ?  What  is 
meant  by  gravity  creaming  ?  Explain  the  principle  of  the  cream  sepa- 
rator. Does  the  separator  remove  more  fat  from  the  milk  than  the 
gravity  process  of  creaming  ?  How  much  fat  is  left  in  separator  skim 
milk  ?  What  can  you  say  of  the  food  value  of  skim  milk  ? 


MILK  AND   ITS  PRODUCTS  363 

Ex.  252.  How  is  butter  made  ?  How  much  fat  does  butter  contain  ? 
What  is  meant  by  the  ripening  of  cream  ?  Why  is  cream  ripened  ? 
What  is  buttermilk  ?  To  what  is  its  acid  taste  due  ?  How  is  artificial 
buttermilk  made  ? 

Ex.  253.  How  is  condensed  milk  made  ?  Examine  a  can  of  con- 
densed or  evaporated  milk.  Dilute  with  twice  its  bulk  of  water. 
Does  it  taste  like  ordinary  milk?  Why  is  sugar  sometimes  added  to 
milk  ?  How  are  milk  powders  prepared  ?  Why  are  they  usually  made 
from  partly  skimmed  milk  ?  If  possible  obtain  a  sample  for  inspection. 

Ex.  254.  Outline  the  method  of  making  American  Cheddar  cheese. 
Rub  a  piece  of  well-ripened  Cheddar  cheese  as  large  as  a  walnut  with  a 
test  tube  full  of  water  and  filter.  To  the  filtrate  add  a  little  tannic  acid 
solution.  Are  there  any  soluble  proteins  in  the  cheese  ?  How  were  they 
formed  ? 

Ex.  255.  How  many  different  kinds  of  cheese  are  on  the  local 
market  ?  Why  can  so  many  kinds  of  cheese  be  made  from  one  kind  of 
milk  ?  How  is  cottage  cheese  made  ?  Is  any  rennet  used  in  this  case  ? 
What  other  uses  are  made  of  casein  ?  What  is  koumiss  ?  Bulgaris  milk  ? 


CHAPTER  XLIII 
TESTING  MILK 

409.  Need  of  a  Test.     It  has  been  stated  that  the  fat  is  by 
far  the  most  valuable  constituent  of  the  milk.     Butter  fat,  as 
it  is  more  commonly  termed,  often  sells  for  over  30  cents  a 
pound  while  the  rest  of  the  milk  may  be  purchased  for  a 
fraction  of  a  cent  a  pound.     Since  milk  varies  in  fat  content 
from  as  low  as  2  per  cent  to  as  high  as  8  per  cent,  it  is  unfair 
to  pay  the  same  price  per  hundredweight  for  all  kinds  of 
milk.     The  creameries  and  factories  now  almost  universally 
pay  for  milk  on  the  basis  of  its  fat  content,  and  consequently 
a  quick,  easy,  and  accurate  method  of  determining  the  fat 
in  milk  is  very  important.     Such  a  test  is  also  of  great  value 
to  the  farmer  in  enabling  him  to  determine  which  cows  in  his 
herd  are  being  kept  at  a  profit  to  him.     A  test  recently  made 
of  a  dairy  herd  showed  that  one  cow  was  yielding  a  profit  of 
over  $80.00  a  year,  while  another  was  being  kept  at  a  loss  of 
$15.00.     By  testing  all  the  cows  and  replacing  those  found 
to  be  unprofitable  with  cows  showing  a  better  test  the  profits 
of  a  dairy  farm  may  be  increased  materially. 

410.  The  Babcock  Test.     The  most  practical  method  for 
testing  milk  for  fat  is  the  one  invented  by  Dr.  Stephen 
Moulton  Babcock  in  1890  and  known  as  the  Babcock  test. 
This  test  has  the  advantage  of  being  simple  and  easily  manipu- 
lated, and  long  use  has  demonstrated  its  great  accuracy. 
The  principle  of  the  test  is  the  separation  of  the  fat  by 
centrifugal  force  in  such  a  way  that  it  can  be  measured. 

364 


TESTING  MILK 


365 


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Eighteen  grams  of  milk  are  treated  with  sulphuric  acid,  which 
dissolves  the  casein  -of  the  milk  and  thus  facilitates  the 
separation  of  the  fat.  The  mixture  is  then  whirled  in  a 
centrifugal  machine,  and  the  fat  col- 
lects on  the  surface  of  the  liquid. 
To  make  the  test  the  apparatus 
shown  in  Figs.  164  and  165  is 
necessary. 

The  test  bottle  is  so  made  that  the 
graduations  on  the  neck  give  the  per- 
centage of  fat  when  the  sample  of 
milk  weighs  18  grams.  The  small 
divisions  represent  0.2  per  cent.  The 
pipette  is  graduated  at  17.6  cubic 
centimeters,  because  experience  has 
shown  that  when  filled  to  the  mark 
the  pipette  will  deliver  just  18  grams 
of  average  milk,  and  it  is  much  easier 
to  measure  the  milk  than  to  weigh  it. 

411.  Sampling  the  Milk.  Milk 
creams  so  readily  that  the  greatest 
care  is  necessary  to  get  a  fair  sample 
of  the  lot  to  be  tested.  The  entire 
amount  should  be  thoroughly  mixed 
by  pouring  several  times  slowly  from 
one  vessel  to  another,  or  by  stirring  J 

the  milk  and  at  the  same  time  taking 
care  that  no  air  is  introduced  into  it. 
Many  errors  are  made  by  not  secur- 
ing a  correct  average  sample.  When 
the  milk  is  thoroughly  mixed,  the 
small  end  of  the  pipette  should  be  FIG.  164. 


\ 


366 


APPLIED   CHEMISTRY 


placed  in  it  and  the  tester  should  suck  on  the  upper  end  until 
the  milk  stands  in  the  tube  about  an  inch  above  the  mark. 
Then  he  should  quickly  slip  a  finger  over  the  upper  end  of  the 
pipette,  easing  the  finger  slightly  until  the  level  of  the  milk  is 
exactly  at  the  mark.  Next  he  should  place  the  lower  end  of 
the  pipette  in  the  neck  of  the  bottle  (Fig.  166),  which  is 

held  in  an  inclined  posi- 
tion, and  allow  the  milk 
to  run  into  the  bottle. 
Finally,  when  the  pipette 
has  completely  drained,  he 
should  blow  out  the  last 
drop  of  milk. 

412.  Adding  the  Acid. 
The  acid  used  should  be 
what  is  known  as  commer- 
cial sulphuric  acid  and 
should  have  a  specific 
gravity  of  about  1.81  to 
1.83.  The  pure  acid  used 
in  the  chemical  laboratory  is  too  strong  and  if  used  will  char 
the  fat.  The  acid  measure  should  be  filled  to  the  mark 
(17.5  cc.)  and  the  acid  should  be  poured  carefully  into  the 
test  bottle,  which  is  held  in  an  inclined  position.  If  this  is 
done  properly,  the  acid  runs  down  the  side  of  the  bottle  and 
stands  in  a  distinct  layer  beneath  the  milk.  When  all  the 
bottles  are  in  readiness,  the  milk  and  the  acid  are  mixed  by 
gently  rotating  the  bottle  until  the  curd  is  all  dissolved  and 
the  liquid  is  uniform  in  color. 

413.  Whirling  the  Bottles.  When  the  milk  and  acid  are 
thoroughly  mixed  the  bottles  are  placed  in  the  centrifuge  (Fig. 
165)  and  whirled  for  five  minutes.  Directions  are  furnished 


FlG.  165.  —  Centrifugal  machine. 


TESTING  MILK 


367 


with  most  machines  which  indicate  the  number  of  turns  of  the 
handle  a  minute  to  produce  the  proper  speed  for  the  bottles. 
With  a  wheel  20  inches  in  diameter  the  correct  speed  is 
900  revolutions  per  minute.  If 
the  diameter  is  greater  or  less 
than  20  inches,  the  speed  must 
be  varied  so  as  to  produce  centrif- 
ugal force  equivalent  to  900 
revolutions  of  the  20-inch 
wheel.  At  the  end  of  the 
five  minutes  the  bottle  is 
filled  with  hot  water  to 
the  base  of  the  neck  and 
Then  it  is  filled  with  hot 


column  is  near  the 
neck  of  the  bottle, 
Experience  has 
and  two  addi- 


whirled  for  two  minutes, 
water  until  the  top  of  the  fat 
top  of  the  graduation  on  the 
and  whirled  for  one  minute, 
shown  that  the  three  whirlings 
tions  of  water  are  necessary  to 
insure  a  clear  column  of  fat 
which  will  permit  of  accurate 
reading.  Unless  there  are  suf- 
ficient bottles  to  fill  the  ma- 
chine, care  must  be  taken  to 
balance  the  weight  exactly  by 
arranging  the  bottles  evenly  on 
opposite  sides  of  the  machine. 
FIG.  166. — Transferring  milk  If  the  number  of  tests  made 

from  pipette  to  test  bottle.         . 

is  odd,  an  extra  bottle  filled  with 

water  is  used  to  preserve  the  balance.     Usually  two  tests 
are  made  of  each  milk,  one  to  check  the  other. 

414.   Reading  the  Fat.     The  fat  must  be  in  a  liquid  con- 
dition in  order  to  make  an  accurate  reading.     After  the 


\ 


368 


APPLIED   CHEMISTRY 


whirling  is  completed  the  bottle  should  be  allowed  to  stand 
for  a  few  minutes  in  water  at  150°  F.  The  fat  should  then 
be  read  from  the  lowest  to  the  highest  point,  the  difference  be- 
tween the  bottom  and  top  readings  being  the  percentage  of 
fat  in  the  milk.  Each  of  the  smaller  divisions  is  two  tenths 

of  a  per  cent,  and  as  the 
fat  can  be  read  between 
the  divisions,  it  is  pos- 
sible to  state  the  per- 
centage to  one  tenth  of 
one   per   cent.      Read- 
ings may  be  more  accu- 
rately made  by  the  use 
of  a  small  pair  of  di- 
viders.     The    dividers 
should  be  so  set  that  the  points  are  at  the 
extreme  top  and  bottom  of  the  fat  column 
(Fig.  167) ;  then  if  the  lower  point  of  the 
divider  is  placed  at  the  zero  mark,  the  upper 
part  will  indicate  the  percentage  of  fat.     Ac- 
curately graduated  test  bottles  and  pipettes 
can  usually  be  easily  obtained.     In   some 
states,  however,   all  the  glassware  for  the 
Babcock  test  is  required  by  law  to  be  veri- 
fied   by    the    experiment  station  or   other 
agency  designated  by  the  legislature  of  the  state. 

415.  Testing  Skim  Milk  and  Buttermilk.  The  skim  milk 
from  the  separator  should  frequently  be  tested  to  make  sure 
that  the  separator  is  thoroughly  skimming  the  milk.  Like- 
wise the  buttermilk  is  tested  to  guard  against  losses  of  fat 
due  to  incomplete  churning.  The  tests  for  these  products  are 
made  in  the  same  way  as  for  whole  milk,  except  that  a  special 


FIG.  167.— 
Reading  the  amount 
of  butter  fat. 


TESTING  MILK 


369 


double-neck  bottle  (Fig.  168)  is  used.  The  milk  and  acid  are 
poured  into  the  bottle  through  the  larger  side  neck.  The 
smaller  neck  in  the  center  of  the  bottle  is 
graduated  to  read  0.05  per  cent  and  may  be 
estimated  between  the  marks  to  0.01  per  cent. 
If  the  separator  is  working  properly,  the  test 
will  not  show  more  than  0.05  per  cent  of  fat 
in  the  skim  milk,  and  good  churning  should 
leave  not  to  exceed  0.2  to  0.3  per  cent  of  fat  in 
the  buttermilk. 

416.  Testing  Cream.  It  is  much  more  diffi- 
cult to  make  an  accurate  test  of  butter  fat  in 
cream  than  in  milk.  Cream  varies  in  fat  con- 
tent from  about  12  per  cent  to  over  40  per 
cent.  As  the  test  bottle  for  milk  reads  to  10 
per  cent  only,  it  is  necessary  to  have  a  special 
bottle  for  cream  (Fig.  169).  The 
bottle  in  common  use  has  a  much 
wider  neck  than  the  milk  bottle 
and  is  graduated  to  30  per  cent. 
The  cream  cannot  be  accurately 
measured,  since  the  pipette  will  skim  milk  and 

*;  buttermilk. 

not  deliver  18  grams   or   cream. 
The  larger  the  percentage  of  fat,  the  lower  the 
weight  of  cream  delivered  by  the  pipette.     To 
make  an  accurate  test  it  is  necessary  to  weigh 
the  cream  instead  of  measuring  it.     This  may 
FIG  169  -     ke    done  on  any  balance,   but  when   a  great 
Bottle  for  test-    many  tests  are  to  be  made  the  specially  de- 

ing  cream. 

signed  balance   (Fig.  170)   will  be  found  con- 
venient.     The  bottle  is  first  balanced;    then  an  18-gram 
weight  is  placed  on  the  side  opposite  to  the  bottle,  and  cream 
EV.  CHEM.  — 24 


FIG.    168.— 
Test    bottle    for 


370 


APPLIED   CHEMISTRY 


is  slowly  run  into  the  bottle  until  it  just  balances  the  weight. 
The  test  is  then  made  in  the  same  manner  as  for  milk.  If 
the  cream  runs  over  30  per  cent  fat,  9  grams  are  used  and 
nine  cubic  centimeters  of  water  are  added  to  the  cream 
in  the  bottle  before  the  acid  is  introduced.  The  reading  is 

then  doubled  to  give  the 
correct  percentage  of  fat. 
A  fairly  accurate  test 
of  the  fat  in  cheese  may 
be  made  by  weighing  out 
9  grams  of  the  sample 
and  placing  it  in  the 
cream  bottle  with  17.6 
cubic  centimeters  of 
warm  water.  The  cheese 
should  be  allowed  to  soak 

FIG.  170.  —  Scales  used  in  cream  test. 

for  an  hour  or  more,  after 

which  the  acid  should  be  added,  and  the  test  should  be  con- 
ducted in  the  usual  way.  To  obtain  the  percentage  of  fat  in 
the  cheese  the  reading  should  be  doubled. 

417.  Composite  Tests.  Where  large  herds  of  cows  are  to 
be  tested,  or  in  the  case  of  creameries  with  a  large  number  of 
patrons,  the  daily  testing  of  the  milk  is  expensive  and  time 
consuming.  In  such  cases  very  good  results  may  be  obtained 
by  use  of  the  composite  test.  A  small  sample  from  each 
milking  is  placed  in  a  bottle  with  a  preservative  such  as 
potassium  bichromate  or  mercuric  chloride  (corrosive  sub- 
limate), and  a  test  of  the  composite  sample  is  made  at  the  end 
of  a  week  or  ten  days.  To  make  such  a  composite  sample 
represent  the  true  average  of  the  various  milkings,  the  amount 
added  to  the  bottle  each  time  should  be  proportional  to  the 
weight  of  the  milk  at  that  milking.  The  entire  sample 


TESTING  MILK  371 

should  be  well  mixed  after  each  addition  of  milk.  The  test 
is  made  as  described  for  ordinary  milk.  Various  devices 
have  been  invented  for  taking  proportional  samples  of  the 
milk.  The  desired  result  may  be  obtained  also  by  taking 
2  cubic  centimeters  of  the  milk  for  the  composite  sample 
for  each  pound  in  weight  of  the  milk  at  each  milk- 
ing. 

418.  Use  of  the  Lactometer.  By  the  use  of  the  lactometer 
and  the  Babcock  test  it  is  possible  to  make  a  fairly  accurate 
estimate  of  the  other  solids  in  the  milk  in  addition  to  the  fat. 
In  the  laboratory,  the  creamery,  and  the  cheese  factory  it  is 
customary  to  speak  of  all  the  solids  of  milk  exclusive  of  the 
fat  as  solids  not  fat  (S.  N.  F.). 

The  lactometer  is  an  apparatus  for  determining  the  specific 
gravity  of  the  milk.  It  consists  of  a  glass  spindle  with  a  long 
slim  neck,  which  will  float  in  milk  or  other  liquid.  The  lower 
the  specific  gravity  of  the  liquid,  the  deeper  the  spindle  sinks 
in  it,  and  the  heavier  the  liquid,  the  higher  the  spindle  floats. 
All  the  solids  found  in  milk  with  the  exception  of  the  fat  are 
heavier  than  water  and,  therefore,  increase  the  specific 
gravity  of  the  milk.  Since  butter  fat,  on  the  other  hand,  is 
lighter  than  water  (specific  gravity  about  0.9),  the  presence 
of  fat  counteracts  the  increase  of  specific  gravity  due  to  the 
other  solids.  Milk  varies  in  specific  gravity  from  1.029  to 
1 .034.  The  lactometer  most  commonly  used  is  the  Quevenne 
lactometer  (Fig.  171).  This  instrument  is  so  graduated  that 
the  figures  on  the  neck  represent  the  second  and  third 
decimal  places  of  the  specific  gravity;  that  is,  32  on  the 
lactometer  is  equivalent  to  a  specific  gravity  of  1.032. 
These  figures  of  the  scale  on  the  neck  of  the  instrument  are 
called  for  convenience  lactometer  degrees.  The  lactometer 
reading  is  made  by  placing  the  milk  in  a  tall  cylinder  and 


372 


APPLIED   CHEMISTRY 


floating  the  lactometer  in  it.  When  the  lactometer  has 
come  to  rest,  the  reading  is  taken  at  the  level  of  the  milk's 
surface.  The  lactometer  gives  the  correct 
reading  only  when  the  temperature  of  the 
milk  is  60°  F.  If  it  is  not  at  that  tem- 
perature, 0.1  should  be  added  to  the  lactom- 
eter reading  for  each  degree  of  temper- 
ature above  60°,  or  the  same  number 
should  be  subtracted  for  each  degree  below. 
In  no  case  should  readings  be  made  if  the 
temperature  varies  more  than  ten  degrees 
from  the  normal  (60°  F.). 

It  has  been  found  by  experiment  that 
the  percentage  of  solids  not  fat  in  a  milk 
is  equal  to  one  fourth  of  the  lactometer 
reading  plus  two  tenths  of  the  percentage 
of  fat.  This  statement  is  briefly  expressed 
1 1  111!  in  what  is  known  as  the  Babcock  formula 

for  solids  not  fat : 


In  the  formula  L  stands  for  the  lactometer 
reading  and  /  for  the  percentage  of  fat. 
For  example,  if  the  lactometer  reading  is 
34  and  the  fat  is  3.5  per  cent,  then 


FIG.  171.  —  Lactom- 
eter. 


The  sample  of  milk,  therefore,  contains  9.2 
per  cent  of  solids  not  fat. 

The  variations  in  the  solids  other  than 
fat  in  milk  are  not  very  great  even  when 
the  different  breeds  of  cows  are  con- 


TESTING  MILK 


373 


sidered.  Adding  water  to  milk  decreases  the  percent- 
age of  solids  not  fat.  The  above  formula,  therefore, 
may  be  used  to  detect  watered  milk.  Many  states  have 
established  by  law  a  standard  for  fat  and  total  solids  in 
milk.  A  common  legal  requirement  is  a  minimum  of 
3.25  per  cent  of  fat  and  9  per  cent  solids  not  fat.  If  the 
solids  not  fat  in  a  milk  are  below  9  per  cent,  the  milk  is 
assumed  to  be  watered.  If  the  fat  falls  below  3.25  per 
cent,  the  milk  is  declared  to  be  skimmed.  By  the  use  of  the 
Babcock  test  and  the  lactometer  it  is  possible,  therefore,  to 
determine  whether  the  milk  has  been  skimmed  or  watered, 
or  both  skimmed  and  watered. 

419.  Acid  Test.  It  is  often  desirable  to  know  the  amount 
of  acid  in  a  sample  of  milk  or  cream.  This  can  easily  be 
determined  by  the  use  of  the 
Farrington  alkali  tablets.  These 
tablets  consist  of  a  carefully 
weighed  quantity  of  sodium  car- 
bonate mixed  with  a  little  phe- 
nolphthalein  indicator  (138).  To 
make  the  test,  dissolve  5  tablets  in 
97  cubic  centimeters  of  water. 
Measure  17.6  cc.  of  the  milk  into 

,  FIG.    172.  — Graduated  cylin- 

a    White    CUp    and    add    the    alkali     der  and  white  cup  used  for  a  test 
i     ,•  i        i  . .      .  .-,  .n       of  milk  or  cream. 

solution  slowly,  stirring  the  milk 

thoroughly  after  each  addition.  The  acid  in  the  milk  will 
at  first  destroy  the  color  of  the  indicator.  The  alkali  solu- 
tion is  added  until  a  pink  color  is  imparted  to  the  milk  which 
does  not  immediately  disappear  upon  stirring.  Each  cubic 
centimeter  of  the  alkali  used  is  equivalent  to  0.01  per  cent  of 
lactic  acid ;  for  example,  if  35  cc.  of  the  alkali  solution  are 
used  the  acidity  of  the  milk  is  said  to  be  0.35  per  cent. 


374  APPLIED   CHEMISTRY 

EXERCISES 

Ex.  256.  Read  carefully  paragraphs  409  to  413  and  test  a  sample  of 
milk  from  home  according  to  the  method  described.  Why  is  it  desirable 
for  the  purchaser  to  know  the  amount  of  fat  in  milk  ?  What  use  can  the 
farmer  make  of  a  simple  method  of  testing  milk  ?  Is  the  Babcock  test 
thoroughly  practical  ? 

Ex.  257.  If  possible  make  a  week's  test  of  each  cow  in  a  herd  in  the 
neighborhood  of  the  school.  Have  a  pint  bottle  for  each  cow.  Place  in 
it  as  much  powdered  potassium  bichromate  as  will  stand  on  a  dime. 
Arrange  for  some  student  to  be  present  at  each  milking,  to  weigh  the  milk 
from  each  cow  and  place  the  sample  in  the  proper  bottle.  Use  2  cc. 
of  milk  for  each  pound  the  cow  produces.  Read  paragraph  417  on  com- 
posite test.  At  the  end  of  the  week  test  each  composite  sample  and 
calculate  how  much  butter  fat  each  cow  produced  during  the  week. 

Ex.  258.  If  the  school  has  the  proper  apparatus,  make  tests  of  skim 
milk,  cream,  and  cheese  as  described  in  the  text. 

Ex.  259.  Determine  the  fat  in  a  sample  of  milk  by  the  Babcock  test, 
and  take  the  lactometer  reading  as  described  in  paragraph  418.  Calcu- 
late the  solids  not  fat  in  the  milk.  \  Assuming  that  the  standard  for 
milk  is  3.25  per  cent  fat  and  9  per  cent  solids  not  fat,  is  a  sample  with  a 
lactometer  reading  of  32  and  a  fat  content  of  3.4  per  cent  watered  ? 

Ex.  260.  Dissolve  5  Farrington  alkali  tablets  in  97  cc.  of  water  in  a 
100  cc.  graduated  cylinder  and  test  a  sample  of  milk  from  home  for 
acidity  according  to  paragraph  419.  If  possible  test  a  sample  of  butter- 
milk in  the  same  way. 


CHAPTER  XLIV 
LEAVENING  AGENTS 

420.  Wheat  Bread.    Bread  of  some  kind  has  been  used  by 
mankind  from  the  earliest  times.     During  the  earlier  periods 
it  consisted  chiefly  of  powdered  meal  and  water,  baked  in 
the  sun  or  on  hot  stones.     This  kind  of  bread  has  the  same 
characteristics  as  modern  hard-tack  or  hoe-cake,  so  far  as 
digestibility  is  concerned.     It  has  great  density,  is  difficult 
to  masticate,  and  presents  but  little  surface  to  the  action  of 
the  digestive  juices.     Such  bread  is  said  to  be  unleavened. 

Very  early  in  the  history  of  the  human  race  leavened 
bread  seems  to  have  been  used.  Experience  must  have 
taught  the  semicivilized  tribes  that  a  light  and  porous  loaf 
was  more  palatable  and  more  digestible  than  a  dense  one, 
for  nearly  all  peoples  now  have  some  method  of  "  raising" 
bread  and  making  it  light. 

421.  To  Make  a  Light  Loaf.     The  incorporation  into  the 
dough  of  bubbles  of  some  kind  of  gas  is  necessary  to  make 
a  light  loaf.    The  possibility   of  a   light,   porous   loaf  of 
wheat  bread   is   due   to   the    gluten  of  the  wheat    (319). 
This  substance,  when  moistened,  forms  a  sticky  elastic  mass, 
which  incloses  the  gas  bubbles  and  prevents  their  escape. 
When  the  bread  is  heated  in  baking,  the  gluten  loses  its  elas- 
ticity, and  becomes  stiffened,  and  retains  its  light  porous 
condition.    Three  general  methods  are  used  to  introduce  the 
gas,  namely,  mechanical,  biological,  and  chemical  methods. 

The  best  known  example  of  the  mechanical  methods  is  the 
"  beaten  biscuit"  of  the  South.  In  this  case  air  is  introduced 

375 


376 


APPLIED  CHEMISTRY 


into  the  dough  by  long-continued  beating,  which  makes  it 
somewhat  porous.  When  the  dough  is  heated  in  the  oven, 
the  air  expands  and  increases  the  porosity  of  the  product. 

The  so-called  aerated  bread  is  made  by  mixing  the  dough 
with  carbonated  water  such  as  is  used  in  soda-water  foun- 
tains. The  mixer  is  so  constructed  that  the  carbon  dioxide 
is  kept  under  high  pressure  during  the  mixing.  When  the 
mixing  is  completed,  the  pressure  is  released  and  the  expan- 
sion of  the  gas  makes  the  dough  light,  as  does  the  further 
expansion  of  the  gas  when  the  dough  is  placed  in  the  oven. 
The  use  of  eggs  for  making  light  cakes,  such  as  sponge  cake 
and  angel  cake,  is  another  example  of  the  mechanical  method. 
The  air  which  is  beaten  into  the  egg  albumin  supplies  the 

bubbles  of  gas  needed  to  make 
the  cake  light. 

422.  Use  of  Yeast  in  Making 
Bread  Light.  Yeast  is  the  sub- 
stance most  commonly  used  to 
make  bread  light.  Condensed 
yeast  consists  of  a  mass  of 
microscopic  plants  (Fig.  173) 
which  grow  or  multiply  rapidly 
in  the  moist  dough  or  sponge, 
especially  if  some  sugar  has  been 
added.  During  its  growth  the 
yeast  plant  secretes  enzymes 
which  bring  about  the  fermen- 
tation of  the  sugars  with  the  formation  of  alcohol  and  carbon 
dioxide  (362) : 


FlQ.  173.  — Yeast  plants. 


CeH^Oe 

glucose 


2  C2H5OH 

alcohol 


2  CO2. 

carbon 
dioxide 


LEAVENING  AGENTS 


377 


When  yeast  is  added  to  the  dough,  and  the  mixture  is  put  in 
a  warm  place,  the  yeast  grows  and  carbon  dioxide  is  produced. 
The  gas  permeates  the  dough,  but  cannot  escape  because  of 
the  tenacious  character  of  the  mass.  As  a  result  the  dough 
rises,  that  is,  it  swells  up  because  of  the  bubbles  of  gas  that 
have  been  formed  within  it. 

After  the  dough  has  risen,  it  is  kneaded  for  the  purpose  of 
breaking  up  the  large  bubbles  and  distributing  the  gas  evenly 


FIG.  174.  —  Cross  sections  of  light  loaves  of  bread.     The  variation  in  size  is  due 
to  differences  in  the  quality  of  the  gluten  in  the  two  flours. 

throughout  the  mixture.  When  the  dough  is  shaped  into 
loaves,  the  fermentation  continues  because  the  yeast  is  still 
growing,  and  the  further  evolution  of  carbon  dioxide  causes 
the  dough  to  rise  again. 

When  the  loaves  are  placed  in  the  oven,  the  first  action  of 
the  heat  expands  the  bubbles  of  carbon  dioxide  and  the  loaf 
is  made  more  porous  and  light.  The  yeast  is  killed,  fermen- 
tation stops,  and  the  alcohol  and  part  of  the  water  are  vapor- 


378 


APPLIED   CHEMISTRY 


ized  and  driven  off.  At  the  same  time  the  starch  grains  are 
ruptured  by  the  heat,  and  the  gluten  is  stiffened  and  loses  its 
elasticity.  The  heat  of  the  oven  (350°  to  400°  F.)  converts 
part  of  the  starch  on  the  outer  edge  of  the  loaf  into  dextrin 
(312),  which  is  one  reason  why  the  crust  of  the  bread  is 
sweeter  than  the  crumb.  The  interior  of  the  loaf  never  gets 
much  above  212°  F.,  because  the  water  in  the  interior  of  the 
loaf  is  being  continually  changed  into  steam. 

423.  Salt-rising  Bread.  This  is  another  example  of  a  bread 
which  is  made  light  by  a  biological  process.  To  make  salt- 
rising  bread,  corn  meal 
and  a  little  baking  soda 
are  mixed  with  warm 
milk.  After  some  hours 
this  batter  begins  to  fer- 
ment and  carbon  dioxide 
is  produced.  Dough-  is 
made  as  for  ordinary 
bread  and  this  mixture 
is  used  in  the  place  of 
yeast.  The  process  of 
handling  is  from  this 
point  the  same  as  that 
described  for  yeast  bread. 
For  a  long  time  the  cause 
of  the  fermentation  in 
salt-rising  bread  was  not 
understood.  It  has  been  discovered  recently,  however,  that 
it  is  due  to  certain  gas-forming  bacteria  that  are  found 
associated  with  the  corn  meal. 

The  ancient  method  of  preserving  a  little  of  the  dough 
from  each  batch  of  bread  to  act  as  the  leaven  for  the  next  is 


FIG.  175.  —  Making  bread  in  the  Orient. 
Kneading  dough  with  leaven. 


LEAVENING  AGENTS  379 

still  followed  in  some  countries.  This  small  bit  of  old  dough 
carries  a  sufficient  number  of  yeast  plants  to  start  the  fermen- 
tation when  it  is  mixed  with  a  new  lot  of  dough,  and  thus 
"  a  little  leaven  leaveneth  the  whole  lump." 

424.  Ammonium  Bicarbonate.     The  use  of  ammonium 
bicarbonate  is  the  simplest  of  the  chemical  methods  of  raising 
bread.     The  ammonium  salt  is  dissolved  in  the  water  used 
in  making  the  dough.     When  the  mass  is  heated,  the  bi- 
carbonate decomposes  into  gaseous  products  : 

NH4HCO3  ->•  NH3  +  H2O  +  CO2. 

The  evolution  of  ammonia  and  carbon  dioxide  and  their 
expansion  when  heated  make  the  bread  porous  and  light. 
In  skillful  hands  this  method  is  very  successful  and  has  the 
advantage  of  leaving  no  solid  residue.  The  ammonia  is 
driven  off  by  the  heat  of  baking. 

425.  Sour  Milk  and  Soda.     These  leavening  agents  have 
long  been  used.     The  lactic  acid  in  the  sour  milk  reacts  with 
sodium  bicarbonate,  also  called  baking  soda,  or  saleratus, 
and  liberates  carbon  dioxide  : 


NaHCO3  ->-  Na.C3H5O3  +  H2O  +  CO,. 

lactic  acid  sodium  lactate 

When  properly  followed,  this  method  of  leavening  is  very 
successful,  but  it  has  the  disadvantage  that  it  is  sometimes 
difficult  to  adjust  the  proportions  of  the  sour  milk  and  soda. 
If  too  much  sour  milk  is  used,  the  product  has  a  sour  taste. 
If  too  much  soda  is  used,  the  excess  of  bicarbonate  is  changed 
by  the  heat  of  the  oven  into  the  normal  carbonate,  which 
gives  a  soapy  taste  to  the  bread  : 

2  NaHCO3  -^  Na2CO3  +  CO2  +  H2O. 


380  APPLIED   CHEMISTRY 

Occasionally  baking  soda  and  hydrochloric  acid  are  used  as 
leavening  agents.  In  this  case  the  soda  is  mixed  with  the 
flour  and  the  hydrochloric  acid  is  added  to  the  water  which  is 
used  in  mixing  the  dough  : 

NaHCO3  +  HC1  -»-  NaCl  +  H2O  +  CO2. 

426.  Baking  Powders.  The  difficulty  of  measuring  the 
exact  amounts  of  acid  and  bicarbonate  when  the  above 
methods  are  used  has  led  to  the  manufacture  of  commercial 
baking  powders.  In  baking  powders  an  acid  salt  is  used 
instead  of  the  free  acid. 

Tartrate  baking  powder  is  composed  of  baking  soda  and 
cream  of  tartar.  These  substances  do  not  react  with 
each  other  while  dry,  but  when  moistened  the  following 
reaction  takes  place  : 

NaHCO3  +  KH  •  CJ^O,  ->-  KNa  •  C4H4O6  +  H2O  +  CO2. 


Phosphate  baking  powders  consist  of  baking  soda  and 
calcium  mono-phosphate,  the  same  compound  that  occurs  in 
the  fertilizers  known  as  acid  phosphate  or  superphosphates. 
The  reaction  in  this  case  is  as  follows  : 

2  NaHCO3  +  CaH4(PO4)2 

->•  CaHPO4  +  Na2HPO4  +  2  H2O  +  2  CO2. 

Alum  baking  powders  are  made  from  baking  soda  and 
ammonium  alum.  The  reaction  here  is  a  deep-seated  one  : 

2  NH4A1(SO4)2  +  6  NaHCO3 

-^2  A1(OH)8  +  3  Na2SO4  +  (NH4)2SO4  +  6  CO2. 


Starch  is  added  in  the  manufacture  of  all  baking  powders  to 
keep  the  materials  dry,  and  to  coat  each  particle  of  the  acid 
salt  and  the  carbonate  in  order  to  prevent  their  acting  upon 


LEAVENING  AGENTS  381 

each  other  while  stored.     From  20  to  25  per  cent  of  starch  is 
sufficient  for  this  purpose. 

427.  Healthfulness  of  Baking  Powders.    It  will  be  seen 
from  the  above  equations  that  one  or  more  products  of 
chemical  reaction  remain  in  the  food  after  baking.     The 
possible  harmful  action  of  these  substances  has  been  the 
subject  of  much  discussion,  but  there  are  few  reliable  ex- 
perimental data  on  the  subject.    There  is  no  reason  to 
believe  that  the  sodium  lactate  produced  when  soda  and 
sour  milk  are  used  has  any  harmful  effects.     Cream  of  tartar 
and  soda  produce  Rochelle  salt,  which  is  a  laxative,  but 
which  probably  has  no  effect  in  the  small  quantities  consumed 
with  the  food.     The  same  statement  may  be  made  regarding 
the  sodium  phosphate  produced  by  the  phosphate  baking 
powders.     More  has  been  said  against  the  alum  baking 
powders  than  any  of  the  others,  and  many  physicians  believe 
that  the  residue  of  aluminum  hydroxide  left  by  them  is  inju- 
rious to  health.     Since  nothing  is  to  be  gained  by  their  use 
except  a  very  small  saving  in  expense,  it  would  be  well  to 
avoid  these  powders,  so  long  as  there  is  a  question  about  it. 

428.  Homemade  Baking  Powder.     A  baking  powder  can 
be  prepared  at  home  from  the  following  ingredients : 

Cream  of  tartar,  dried .'  .    .     1  pound 

Baking  soda |  pound 

Starch         ^  pound 

Thoroughly  dry  the  starch  and  cream  of  tartar  in  a  warm 
(not  hot)  oven,  Divide  the  starch  into  two  parts,  and  mix 
the  soda  with  one  part,  and  the  cream  of  tartar  with  the 
other.  Then  mix  the  whole  thoroughly  and  keep  the  mixture 
in  cans  or  bottles  in  a  dry  place. 

429.  Shortening.     Pie  crust  and  similar  forms  of  pastry 
are  not  leavened.    Instead  the  flour  is  so  treated  that  when 


382  APPLIED   CHEMISTRY 

heated  it  crumbles  readily  into  thin  flakes.  This  is  accom- 
plished by  the  method  known  by  the  housewife  as  shortening, 
and  consists  in  mixing  a  fat,  such  as  butter,  lard,  or  oil,  with 
the  flour  in  making  the  dough.  The  fat  destroys  the  elas- 
ticity of  the  gluten,  making  it  break  off  short  when  worked 
instead  of  allowing  it  to  remain  tenacious,  as  it  is  in  ordinary 
dough.  The  result  of  this  treatment  is  a  flakiness  that  has 
the  effect  of  exposing  a  large  surface  to  the  digestive  fluids ; 
but  this  good  effect  is  counteracted  by  the  presence  of  the 
large  amount  of  fat,  which  produces  a  greasy  surface  that 
interferes  with  the  action  of  the  digestive  juices  upon  the 
proteins  and  carbohydrates.  Because  of  its  expansion  under 
the  heat  of  the  oven,  the  air  folded  into  the  dough  is  probably 
another  factor  in  making  the  pastry  light  and  flaky. 

EXERCISES 

Ex.  261.  Is  the  use  of  wheat  bread  of  modern  origin?  How  was 
the  first  bread  probably  made  ?  Why  is  a  light  loaf  desirable  ?  What 
is  necessary  to  make  a  light  loaf  ?  What  is  the  function  of  the  gluten 
in  bread  making?  What  change  takes  place  in  the  gluten  when  the 
bread  is  baked  ? 

Ex.  262.  .What  is  the  principle  underlying  the  making  of  beaten 
biscuits?  How  is  aerated  bread  made?  What  makes  it  light?  Ex- 
plain how  eggs  make  possible  the  production  of  a  light  cake  such  as 
sponge  cake. 

Ex.  263.  Explain  how  the  use  of  yeast  makes  a  light  loaf  possible. 
Devise  an  experiment  to  show  that  carbon  dioxide  is  given  off  by  the 
sponge  in  bread  making.  Explain  the  formation  of  the  numerous  holes 
in  a  loaf  of  bread.  Why  does  the  baked  loaf  retain  its  shape  when  the 
dough  will  not? 

Ex.  264.  What  makes  the  bread  light  in  the  case  of  salt-rising  bread  ? 
Why  is  the  corn  meal  added?  Explain  the  ancient  method  of  saving 
the  leaven  from  one  baking  to  another. 

Ex.  265.  When  ammonium  carbonate  is  used  to  raise  bread,  what 
chemical  change  takes  place  ?  What  advantage  has  ammonium  carbon- 


LEAVENING  AGENTS  383 

ate  over  other  baking  powders  ?  Explain  the  use  of  baking  soda  with 
sour  milk.  Add  some  baking  soda  to  sour  milk  at  home  and  prove  that 
carbon  dioxide  is  given  off.  What  is  the  chief  difficulty  in  using  these 
materials  ?  What  happens  if  too  much  soda  is  used  ? 

Ex.  266.  Moisten  samples  of 'baking  powder  with  water  and  de- 
termine whether  carbon  dioxide  is  evolved.  What  are  the  three  general 
types  of  baking  powders  on  the  market?  Obtain  several  samples  of 
baking  powder  and  test  to  see  if  they  are  tartrate,  phosphate,  or  alum 
powders,  as  follows  : 

(a)  Test  for  phosphate  by  burning  the  powder  to  destroy  the  starch, 
and  then  heat  with  a  little  nitric  acid  and  add  ammonium  molybdate 
reagent. 

(6)  Test  for  alum.  Dissolve  in  water  and  filter.  To  the  filtrate  add 
a  little  hydrochloric  acid  and  some  bafium  chloride  solution.  A  white 
precipitate  indicates  alum.  (Note.  This  is  really  a  test  for  sulphates, 
but  as  alum  is  the  only  sulphate  used  in  baking  powders  it  serves  the 
purpose.) 

(c)  There  is  no  easy  test  for  tartrate,  but  if  the  powder  is  not  a  phos- 
phate nor  an  alum  powder,  it  is  undoubtedly  made  with  tartrate. 

Ex.  267.  What  is  the  residue  left  in  the  food  when  sour  milk  and 
soda  are  used?  When  cream  of  tartar  and  soda  are  used?  When  a 
phosphate  powder  is  used  ?  In  case  of  an  alum  powder  ?  Is  any  objec- 
tion raised  to  any  of  these  powders  ?  What  type  of  baking  powder  do 
you  use  at  home  ? 

Ex.  268.  Have  the  class  make  a  baking  powder  according  to  the 
directions  in  paragraph  428.  Divide  among  the  members  of  the 
class  and  have  it  tested  in  their  homes.  Call  for  reports. 

Ex.  269.  (Teacher)  From  a  cupful  of  flour  prepare  gluten  as  in 
exercise  197.  Note  the  elasticity  of  the  gluten.  Now  work  thoroughly 
into  the  gluten  a  good-sized  piece  of  lard.  What  effect  does  the  fat 
have  on  the  elasticity  of  the  gluten?  What  is  meant  by  shortening? 
How  does  it  make  pastry  light  and  flaky?  Why  is  pastry  hard  to 
digest? 


CHAPTER  XLV 

FOOD   PRESERVATION,   ANTISEPTICS,   AND   DISIN- 
FECTANTS 

430.  Why  Foods  Spoil.  The  fermentation  and  decay  of 
foods,  which  render  them  unfit  for  consumption,  are  due  to 
the  growth  of  molds  and  microorganisms  such  as  yeast  and 
bacteria  (Fig.  176).  These  organisms  act  upon  the  carbo- 
hydrates and  produce  alcohol,  carbon  dioxide,  and  various 
organic  acids.  Some  of  the  bacteria  cause  the  decay  or  pu- 
trefaction of  the  proteins,  with  the  production  of  the  foul 


FIG.  176.  —  Bacteria.     1.  Typhoid  fever.    2-5.  Forms  of  bacteria  found 

in  milk. 

odors  so  noticeable  in  decaying  meat  and  other  high 
protein  foods.  Some  of  these  organisms  produce  from 
the  proteins  poisonous  substances  which  are  known  as 
ptomaines  (326).  Without  some  method  of  preserving 
food  the  human  diet  would  at  least  lack  the  variety  that 
is  now  possible.  Molds,  yeast,  and  bacteria  are  present 
everywhere  in  the  air,  especially  when  the  air  is  dust 
laden.  While  foods  should  be  protected  from  dust  and 
dirt,  which  always  contain  bacteria,  it  is  practically  impos- 
sible to  prevent  entirely  their  entrance  into  the  food  ma- 

384 


FOOD  PRESERVATION  AND   DISINFECTANTS     385 


terials.     Hence  if  food  is  to  be  preserved,  some  method  must 
be  used  to  destroy  these  organisms  or  to  prevent  their  growth. 

431.  Preservation  by  Drying.     The  conditions  necessary 
for  the  growth  of  the  organisms  that  cause  foods  to  spoil  are 
the  presence  of  moisture  and  warmth.     Materials  that  are 

Very  dry,  such  as 
flour  and  crackers, 
will  keep  indefinitely 
if  not  allowed  to  be- 
come damp.  The 
drying  of  meats, 
fruits,  and  vegetables 
has  been  practiced 
from  early  times. 
Formerly  these  food 
products  were  all 
dried  in  the  sun ;  but 
now  many  devices 
are  in  use  for  the 
artificial  drying  of 
these  materials. 

432.  Refrigeration. 


FIG.  177.  —  The  preservation  of  foods  by  diying. 


A  low  temperature 
retards  the  growth 
of  the  organisms  that  produce  fermentation  and  decay,  and 
consequently  the  lower  the  temperature  at  which  foods  are 
held  the  longer  they  will  keep.  The  cold  storage  business, 
which  has  grown  to  enormous  proportions,  is  based  upon  this 
principle.  Food  substances  that  can  be  frozen  without 
injury  can  be  kept  almost  indefinitely  in  the  frozen  state. 
Since  cold  and  freezing  do  not  kill  the  bacteria  outright  but 
merely  prevent  their  growth,  perishable  substances  when 
EV.  CHEM. — 25 


386  APPLIED   CHEMISTRY 

removed  from  cold  storage  will,  of  course,  spoil  the  same  as 
fresh  materials.  The  temperature  produced  in  the  home 
ice  box  or  refrigerator  is  not  low  enough  to  retard  the  decom- 
position of  food  for  very  long  periods. 

433.  Preserving  in  Strong  Solutions.     Yeasts  and  bacteria 
cannot  grow  in  concentrated  solutions.     When  the  solution 
contains  more  than  20  per  cent  of  solids,  the  osmotic  action 
of  the  solution  is  so  great  that  it  extracts  water  from  the  living 
cell  and  causes  the  protoplasm  to  collapse,  resulting  in  the 
death  of  the  cell.     The  method  of  preserving  meats  and  vege- 
tables by  placing  them  in  strong  brine  depends  upon  this  fact. 
If  the  brine  is  too  weak,  the  organism  can  grow  and  the  food 
spoils.     Dry  salting  of  meats  is  another  instance  of  the  same 
method  of  preservation.     The  salt  rubbed  into  the  meat  dis- 
solves in  the  moisture  present  and  forms  a  brine  which  is 
strong  enough  to  prevent  the  growth  of  bacteria. 

Approximately  fifty  per  cent  of  jelly  and  jam  consists  of 
the  sugar  added  in  their  manufacture.  Sugar  is  a  food  for 
bacteria  and  yeast  when  in  dilute  solution,  but  in  the  con- 
centration used  in  jellies  and  jams  it  destroys  these  organisms 
by  its  great  osmotic  action.  The  heating  incident  to  pre- 
paring these  foods  also  assists  in  destroying  these  organisms. 

434.  Preservation  by  Heat.     The  organisms  that  cause 
fermentation  and  decay  in  foods  are  killed  at  the  temperature 
of  boiling  water  if  the  heating  is  continued  for  some  time. 
Foods  that  are  boiled  or  otherwise  heated  to  this  temperature 
will,  therefore,  keep  indefinitely  if  properly  protected  from 
further   infection.     The   canned   vegetables   which   occupy 
such  a  large  place  in  the  modern  dietary  are  preserved  by  this 
method.     The  vegetables  are  placed  in  cans  and  heated  and 
the .  cans  are  sealed  while  very  hot.     The  heating  is  commonly 
done  under  pressure  to  make  the  temperature  still  higher  and 


FOOD  PRESERVATION  AND  DISINFECTANTS     387 

the  destruction  of  the  organisms  more  certain.  If  the  ends 
of  the  can  bulge  outward  or  if  gas  escapes  under  pressure 
when  the  can  is  punctured  it  is  a  sign  that  the  food  in  the  can 
has  fermented.  Such  goods  should  be  rejected. 

Bottled  fruits  and  vegetables  prepared  at  home  depend 
upon  the  same  principle  for  their  preservation.  If  the  bottles 
and  the  tops  and  the  rubbers  are  sterilized  and  the  foods  are 
completely  sterilized  by  cooking,  they  will  keep  indefinitely. 
If  any  of  the  germs  are  undestroyed,  fermentation  will  subse- 
quently take  place.  Some  bacteria  form  spores  with  very 
thick  cell  walls  which  are  resistant  to  heat.  Unless  all 
these  are  killed  they  may  later  germinate  and  cause  the  food  to 
ferment.  They  may  be  killed  by  long-continued  heating, 
or  by  the  very  high  temperature  produced  under  pressure. 
As  too  long  a  period  of  boiling  injures  the  quality  of  some 
of  the  food  products,  the  method  of  intermittent  heating  is 
sometimes  used.  In  this  method  the  food  is  heated  for  short 
periods  at  three  different  times,  a  day  or  two  apart.  The 
spores  germinate  in  the  intervals  between  the  heatings  and 
thus  may  easily  be  killed.  Small  pressure  heaters  suitable 
for  use  in  the  home  are  now  on  the  market,  and  their  use 
makes  the  canning  process  more  reliable. 

A  modification  of  the  canning  procedure  known  as  the 
cold  pack  method  (Fig.  178)  is  growing  in  favor  and  is  largely 
used  by  the  members  of  the  girls'  canning  clubs.  In  this 
method  the  material  is  first  blanched,  that  is,  cooked  for  a 
short  time  in  boiling  water  or  steam.  It  is  quickly  dipped 
into  cold  water,  and  afterward  packed  into  hot  jars  which 
are  then  filled  with  boiling  water,  immersed  in  hot  water, 
and  boiled  for  periods  of  from  ten  minutes  to  three  hours, 
depending  upon  the  material  that  is  being  canned. 

It  has  been  stated  that  temperatures  of  140°  to  150°  F.  will 


388 


APPLIED   CHEMISTRY 


kill  most  of  the  germs  and  delay  the  spoiling  of  foods.     About 
the  only  practical  application  is  the  pasteurizing  of  milk. 

435.  Chemical  Preservatives.  Sometimes  chemicals  are 
added  to  foods  to  prevent  their  fermentation.  The  chem- 
icals most  commonly  used  are  borax,  boric  acid,  benzoic  acid, 
sodium  benzoate,  salicylic  acid,  sodium  salicylate,  formalde- 
hyde, sulphur  dioxide,  and  sodium  sulphite.  The  use  of  some 
of  these  substances  is  illegal,  while  others  may  be  legally  used 


vw  kft>« 


ilfisK 


FIG.  178.  —  Preserving  by  the  cold  pack  canning  method. 

if  their  presence  is  indicated  on  the  package.  The  harmful- 
ness  of  some  of  these  preservatives  is  a  matter  of  dispute ;  but 
as  their  use  is  unnecessary,  it  is  best  to  avoid  all  canned  or 
bottled  products  containing  any  preservative.  The  use  of 
these  chemicals  makes  it  possible  to  can  poor  products  under 
careless  and  unsanitary  conditions.  With  good  vegetables 
or  fruits  and  clean  factory  conditions  the  use  of  chemical 
preservatives  is  absolutely  unnecessary,  and  it  seems  reason- 
able to  believe  that  any  chemical  that  will  prevent  the 
growth  of  bacteria  will  also  interfere  with  digestion.  The 


FOOD  PRESERVATION  AND  DISINFECTANTS     389 

use  of  formaldehyde  in  milk  is  especially  pernicious,  as  milk 
is  so  largely  used  in  feeding  babies  and  young  children.  A 
sample  of  milk  or  moist  food  product  which  keeps  a  long  time 
when  exposed  to  the  air  probably  contains  a  chemical  pre- 
servative. Such  products  should  not  be  used  as  foods. 

436.  Antiseptics  are  substances  that  check  the  growth  of 
bacteria.     They  may  not  kill  all  the  bacteria  present,  how- 
ever.    Some  of  the  same  substances  that  are  used  as  food 
preservatives  are  also  employed  as  antiseptics.     Most  of  the 
antiseptic  mouth  washes,  such  as  listerine,  have  borax  and 
boric  acid  as  their  basis,  associated  usually  with  thymol  or 
some  other  aromatic  antiseptic.     A  solution  of  boric  acid  is 
often  used  also  as  an  antiseptic  eye  wash.     Various  anti- 
septics are  used  also  as  a  wash  or  dressing  for  wounds  in  order 
to  destroy  any  bacteria  which  may  have  found  their  way  into 
the  wounds.     Such  bacteria  as  the  tetanus  germ  that  pro- 
duces lockjaw  are  often  present  in  dirt  and  may  be  introduced 
into   a  wound.     Hydrogen   peroxide,   a   weak   solution   of 
carbolic  acid,  listerine,  or  even  alcohol  may  be  employed  as 
antiseptic  applications  in  such  cases.     Every  cut  or  other 
break  in  the  skin  should  be  immediately  washed  with  one  of 
the  above  solutions,  especially  if  any  dirt  is  known  to  have 
entered  the  wound.     Physicians  often  dress  wounds  with 
iodoform,  which  is  another  antiseptic. 

437.  Disinfectants,  or  germicides,  are  substances  that  will 
kill  all  bacteria.     Some  of  these  materials  are  antiseptics 
in  dilute  solutions  and  disinfectants  in  greater  concentration. 
Disinfectants   are   used   to   destroy   bacteria   and   thereby 
remove  the  danger  of  infection.      A  solution  of  mercuric 
chloride  (corrosive  sublimate)  is  quite  commonly  used  as  a 
disinfectant,    as    is    also    strong   carbolic   acid.     Bleaching 
powder,  or  chloride  of  lime   (124),  has  strong  germicidal 


390 


APPLIED   CHEMISTRY 


properties  because  of  the  chlorine  liberated  from  it.  All 
articles  used  in  cases  of  contagion  should  be  immersed  in  a 
disinfectant  solution  before  being  removed  from  the  sick 
room.  Heat  is  one  of  the  best  disinfectants,  and  articles  that 
will  stand  boiling  in  water  can  best  be  sterilized  in  that  way. 
Sulphur  dioxide  has  long  been  used  for  disinfecting  bed- 
rooms after  cases  of  contagious  diseases.  It  is  often  formed 
by  burning  sulphur  in  the  room;  or  the  liquid  sulphur 
dioxide,  which  may  be  purchased  in  small  metal  cylinders, 
is  used.  Both  chlorine  and  sulphur  dioxide  are  bleaching 
agents,  and  their  use  as  household  disinfectants  is  largely 
superseded  by  the  use  of  formaldehyde,  which  is  a  powerful 
germicide  and  has  no  bleaching  action  (287).  Specially 

devised  machines  for  man- 
ufacturing formaldehyde 
on  the  ground  are  used 
when  large  areas  are  to  be 
fumigated. 

For  use  in  disinfecting 
on  a  smaller  scale,  the 
solid  substance  sold  under 
such  names  as  formacone 
or  paraform  is  convenient. 
This  is  a  condensation 
product  of  formaldehyde. 
Under  certain  conditions  several  molecules  of  formalde- 
hyde can  be  made  to  combine  to  form  the  white  solid  sub- 
stance mentioned  above,  which  is  known  to  the  chemist 
as  paraformaldehyde.  This  substance  is  made  into  tablets 
or  candles  and  when  heated  or  boiled  with  water  it  is  changed 
back  into  gaseous  formaldehyde,  and  thus  provides  an  easy 
and  efficacious  method  of  disinfecting  a  room  after  sickness. 


FIG.  179.  —  A  formacone  candle. 


FOOD  PRESERVATION  AND   DISINFECTANTS     391 

EXERCISES 

Ex.  270.  What  causes  foods  to  spoil  ?  How  generally  are  molds  and 
bacteria  distributed?  How  does  a  knowledge  of  food  preservation 
affect  our  dietary?  What  conditions  are  necessary  for  the  growth  of 
molds  and  bacteria  ?  Why  do  not  perfectly  dry  foods  spoil  ?  What  can 
you  say  of  drying  as  a  method  of  food  preservation  ?  What  effect  has 
cold  on  the  keeping  of  food  ?  Does  freezing  kill  the  bacteria  outright  ? 

Ex.  271.  How  does  a  strong  brine  prevent  the  fermentation  of 
foods  ?  If  the  brine  is  too  weak  what  happens  ?  Explain  the  preserva- 
tion of  meat  by  dry  salting.  Why  are  jellies  and  jams  so  easily  kept  ? 
Would  fruits  keep  if  only  a  little  sugar  was  added  to  them  ? 

Ex.  272.  Explain  the  theory  of  keeping  fruits  and  vegetables  by 
canning.  Why  do  factories  heat  them  under  pressure?  Why  should 
canned  goods  be  discarded  if  the  can  bulges  outward  ?  Why  are  vege- 
tables sometimes  heated  on  three  different  days  ?  Does  anyone  in  your 
neighborhood  use  a  pressure  heater  in  canning  fruits  and  vegetables  ? 
What  is  meant  by  the  cold  pack  method?  Write  to  your  Agricultural 
College  for  bulletins  describing  the  cold  pack  method  and  try  canning 
some  kind  of  vegetable  by  this  method. 

Ex.  273.  What  chemicals  are  sometimes  used  as  food  preservatives  ? 
What  do  you  think  of  the  policy  of  using  these  chemicals  ?  Are  they 
necessary  with  good  materials  ?  Examine  the  cans  and  bottles  that  come 
into  your  home  and  see  if  any  of  them  state  that  a  preservative  is  used. 

Ex.  274.  To  a  pint  of  milk  add  two  or  three  drops  of  formaldehyde. 
Set  the  bottle  aside  and  see  how  long  it  takes  the  milk  to  sour.  Why 
should  milk  be  regarded  with  suspicion  if  it  keeps  too  long  ?  Test  sus- 
pected milk  for  formaldehyde  as  follows :  Fill  a  test  tube  one  third  full 
of  the  milk.  Hold  the  tube  in  an  inclined  position  and  carefully  pour 
down  the  side  of  the  tube  a  little  sulphuric  acid  to  which  has  been  added 
a  drop  of  ferric  chloride  solution.  If  formaldehyde  is  present  a  violet 
color  forms,  where  the  acid  and  milk  came  into  contact. 

Ex.  275.  What  is  meant  by  antiseptics  ?  Of  what  are  most  of  the 
antiseptic  washes  made  ?  Why  is  it  dangerous  to  get  dirt  into  a  wound  ? 
How  should  cuts  be  treated  ?  Name  some  of  the  more  common  anti- 
septics. What  is  a  disinfectant  ?  In  what  way  does  it  differ  from  an 
antiseptic  ?  Name  some  disinfectants.  Why  is  formaldehyde  now  used 
in  place  of  sulphur  dioxide  and  chlorine? 


CHAPTER  XLVI 
TEXTILES,  DYEING,  AND   BLEACHING 

438.  ALL  the  fabrics  ordinarily  employed  in  making  cloth- 
ing are  composed  of  one  or  more  of  the    four   commonly 
used  fibers  :  cotton,  linen,  wool,  or  silk.    Of  these  fibers,  cot- 
ton and  linen  are  of  vegetable  origin,  while  wool  and  silk  are 
derived  from  animal  sources. 

439.  Cotton.     Cotton  fibers  are  the  seed  hairs  of  the  cotton 
plant.     Each  seed  hair  is  a  long,  tubular,  single  plant  cell, 
which  during  growth  is  full  of  protoplasm.     As  the  seed 
ripens,  the  protoplasm  disappears,  the  tube  collapses,  and  the 
hair  becomes  twisted  into  a  spiral  as  shown  in  Figure  180. 


Cotton 


Wool 
FIG.  180.  —  Textile  fibers. 


Silk 


Cotton  when  pure  consists  almost  wholly  of  cellulose.  It  is 
not  readily  attacked  by  alkalies,  but  is  easily  destroyed  by 
acids  (313).  Cotton  fabrics  are  used  in  larger  quantities 
than  those  made  from  any  other  fiber. 

440.  Mercerized  Cotton.  When  cotton  is  treated  with  a 
concentrated  solution  of  sodium  hydroxide,  it  contracts  to 
about  three  fourths  of  its  original  length,  and  is  converted 

392 


TEXTILES,   DYEING,   AND  BLEACHING          393 

into  a  new  substance  called  alkali  cellulose.  If  this  material 
is  now  stretched  to  the  original  length  of  the  cotton  and  then 
thoroughly  washed  and  dried,  the  fiber  takes  on  a  silky 
sheen.  Mercerized  cotton  is  stronger  than  ordinary  cotton 
and  has  a  greater  affinity  for  dyes. 

Cotton  is  treated  also  in  a  number  of  ways  to  give  the 
fiber  the  appearance  of  silk.  Most  of  the  artificial  silks, 
such  as  near  silk,  chardonnet  silk,  and  viscose  silk,  are  manu- 
factured from  cotton  fiber  by  special  treatments. 

441.  Linen  also  is  almost  pure  cellulose.     It  is  made  from 
the  fibers  of  the  straw  of  the  flax  plant.     The  straw  is  placed 
in  stagnant  water  where  it  partially  decays,  this  decay  making 
it  possible  to  separate  the  fibers  from  the  other  parts  of  the 
plant   by  mechanical   means.     This   process   is   known   as 
retting.     Natural  retting  is  sometimes  replaced  by  so-called 
chemical  retting,  a  process  in  which  the  fibers  are  separated 
by  means  of  dilute  acids  instead  of  by  the  slower  process  of 
decay.     The  fiber  of  linen  is  longer  and  stronger  than  that 
of  cotton;  it  has  more  luster,  and  is  a  better  conductor  of 
heat.     Linen  is  also  more  readily  destroyed  by  strong  alkalies 
and  by  chlorine  and  other  oxidizing  agents. 

442.  Wool  is  the  hair  of  the  sheep  or  goat.     There  are 
several  varieties  of  wool,  the  kind  depending  upon  the  animal 
from  which  it  is  obtained.     Cashmere  comes  from  the  Tibet 
goat,  mohair  from  the  Angora  goat,  and  alpaca  from  the 
llama.     Not  all  dress  goods  bearing  these  names  come  from 
the  proper  sources,  however,  since  the  peculiar  characteristic 
of  each  can  be  imitated  in  common  wool. 

Wool  is  composed  of  nitrogenous  substances  containing  sul- 
phur and  when  burned  gives  off  the  peculiar  odor  of  burned 
hair.  All  wool  fibers  have  an  outer  layer  of  flat  cells  the 
edges  of  which  project  outward,  making  a  saw-tooth  appear- 


394 


APPLIED   CHEMISTRY 


ance  under  the  microscope  (Fig.  180).  When  the  wool 
fibers  are  beaten  together,  this  peculiar  structure  causes  them 
to  interlock,  and  thus  makes  possible  the  manufacture  of  such 
materials  as  felt.  Wool  is  readily  attacked  by  alkalies ;  even 
dilute  solutions  of  sodium  hydroxide  cause  it  to  dissolve. 
On  the  other  hand,  acids  affect  cotton  much  more  readily 

than  they  do  wool. 
Much  of  the  cloth  that 
is  sold  as  woolen  goods 
is  a  mixture  of  wool 
and  cotton  fibers.  It 
is  a  simple  matter  to 
detect  such  a  mixture  ; 
for  if  the  cloth  is  placed 
in  a  dilute  solution  of 
sodium  hydroxide,  the 
wool  will  dissolve, 
while  the  cotton  will 
remain.  An  all  wool 
cloth  will  dissolve  com- 
pletely (Fig.  181). 
As  wool  is  comparatively  expensive,  old  worn  woolen  cloth 
is  picked  to  pieces,  woven  again  into  yarn,  and  used  to  make 
new  cloth.  A  fabric  made  in  this  way  is  called  shoddy.  It 
has  a  short  fiber  and,  consequently,  is  weak  and  will  not  wear 
as  well  as  new  wool. 

443.  Silk  is  obtained  from  the  cocoon  of  the  silkworm. 
The  cocoons  are  heated  to  70°  C.  to  kill  the  worms  and  then 
are  washed  in  warm  water  to  soften  the  silk  glue  so  that  the 
fibers  may  be  reeled.  The  fibers  from  several  cocoons  are 
twisted  together  in  the  reeling  process  and  thus  a  silk  thread 
is  obtained.  Silk  thread  has  a  beautiful  luster  and  a  high 


FIG.  181.  —  Test  for  all  wool  fabrics  with  sodium 
hydroxide.  The  all  wool  cloth  appears  on  the  left ; 
that  of  mixed  wool  and  cotton  on  the  right. 


TEXTILES,    DYEING,  AND  BLEACHING          395 

tensile  strength.  It  is  a  nitrogenous  substance  containing 
no  sulphur,  differing  in  this  respect  from  wool.  Silk  is  some- 
what more  resistant  than  wool  to  the  action  of  alkalies,  but 
is  more  readily  attacked  by  acid  and  is  very  sensitive  to  the 
action  of  chlorine  and  other  oxidizing  agents. 

444.  Dyeing.  The  animal  and  plant  fibers  differ  greatly 
in  their  behavior  toward  dyestuffs.  Many  of  the  substances 
used  to  dye  cloth  are  either  acid  or  basic  in  character.  The 
animal  fibers  resemble  the  proteins  in  chemical  behavior  and 
like  the  proteins  have  the  power  of  uniting  chemically  with 
the  acid  or  basic  dye  and  forming  a  colored  compound  that  is 
insoluble  in  water.  It  is,  therefore,  a  comparatively  easy 
matter  to  dye  silk  or  woolen  goods. 

Cotton  and  linen,  on  the  other  hand,  are  largely  cellulose, 
which  has  no  chemical  affinity  for  the  dyes.  Cellulose  is 
stained  by  the  dyes,  but  the  color  is  not  fast.  Cotton  and 
linen  are  dyed  by  first  introducing  into  the  fiber  an  insoluble 
substance  that  will  unite  with  the  dye  and  hold  the  color  fast. 
A  common  method  of  procedure  is  first  to  immerse  the  cloth 
in  a  solution  of  aluminum  chloride  or  sulphate,  or  a  bath  of 
ordinary  alum;  then  when  the  cloth  is  placed  in  ammonia 
water,  the  following  reaction  takes  place  : 

A1C13  +  3  NH4OH  -*-  A1(OH)3  +  3  NH4C1. 

The  aluminum  hydroxide  (Al(OH)j)  is.  insoluble  and  ad- 
heres to  the  fibers  of  the  cloth.  If  the  cloth  is  now  immersed 
in  the  dye  solution,  the  aluminum  hydroxide  unites  with  the 
dye  and  holds  the  color  fast.  Materials  used  in  this  way  to 
fasten  the  color  in  fabrics  are  called  mordants.  Salts  of 
aluminum  are  the  more  common  mordants,  although  salts 
of  tin,  iron,  and  chromium  are  largely  used,  as  well  as  tannic 
acid,  the  latter  especially  for  the  basic  dyes. 


396  APPLIED   CHEMISTRY 

445.  Direct  Dyes.     A  few  years  ago  it  was  thought  to  be 
impossible  to  dye  cotton  and  linen  without  the  use  of  a 
mordant  to  hold  the  color  to  the  fiber.     Recently,  however, 
a  number  of  dyes  have  been  discovered  that  adhere  to  the 
cotton  and  linen,  and  some  of  them  possess  a  satisfactory 
permanence.     These  direct  dyes   are  used  extensively  in 
dyeing  mixed  goods  consisting  of  cotton  and  wool  or  cotton 
and  silk.     The  colors  are  not  so  fast  as  those  used  with  a 
mordant,  and  they  are  much  more  readily  affected  by  strong 
soaps  and  alkalies. 

446.  Bleaching.     The  differences  in  the  chemical  com- 
position of  the  various  textile  fibers  and  of  the  coloring 
materials  to  be  destroyed  make  it  impossible  to  use  a  single 
method  for  bleaching  cotton,  linen,  wool,  and  silk. 

Cellulose  is  capable  of  withstanding  the  action  of  chlorine, 
as  well  as  that  of  weak  acids  and  alkalies.  Cotton,  therefore, 
is  almost  universally  bleached  by  means  of  chlorine  derived 
from  bleaching  powder  (124).  The  chlorine  is  liberated 
from  the  bleaching  powder  by  a  weak  solution  of  sulphuric 
acid,  and  the  chlorine  reacts  with  water  to  liberate  oxygen 
as  follows : 

H2O  +  2  Cl  -^  2  HC1  +  O. 

The  bleaching  is  really  due  to  the  destruction  of  the  coloring 
matter  by  the  nascent  oxygen  (81)  and  is,  therefore,  an 
oxidation  process. 

Linen  fibers  are  more  sensitive  to  the  action  of  chlorine 
than  are  those  derived  from  cotton.  Great  care,  therefore, 
must  be  exercised  not  to  weaken  unduly  the  fiber  when 
bleaching  with  chlorine.  The  ancient  method  of  bleaching 
linen,  which  is  still  in  use  in  many  parts  of  the  Old  World, 
consists  in  steeping  the  cloth  in  a  weak  alkaline  solution  and 


TEXTILES,   DYEING,  AND  BLEACHING          397 

then  spreading  it  on  the  grass  to  bleach  in  the  sunlight.  The 
cloth  is  sprinkled  from  time  to  time  with  water.  It  is  finally 
dipped  into  buttermilk  and  then  washed  with  soap  and  water. 

Wool  and  silk  should  never  be  bleached  with  chlorine. 
The  bleaching  is  usually  accomplished  by  means  of  sul- 
phurous acid  or  sodium  peroxide.  When  sulphurous  acid 
is  used,  the  goods  are  moistened  and  then  subjected  to  the 
action  of  sulphur  dioxide  produced  by  burning  sulphur  (63). 

When  sodium  peroxide  is  used,  the  goods  are  first  immersed 
in  a  dilute  solution  of  sulphuric  acid,  and  then  the  sodium 
peroxide  is  added.  This  substance  reacts  with  the  acid  to 
produce  hydrogen  peroxide  (45)  thus : 

Na2O2  +  H2SO4  ->-  Na2SO4  +  H2O2. 

The  hydrogen  peroxide  readily  decomposes,  liberating 
oxygen  (81),  which  is  the  bleaching  agent. 

EXERCISES 

Ex.  276.  Examine  cotton  fibers  under  the  microscope  and  make  a 
drawing  of  them.  What  is  the  chemical  composition  of  pure  cotton? 
Pour  20  cc.  of  sulphuric  acid  into  10  cc.  of  water.  When  the  mixture 
is  cool,  place  a  piece  of  cotton  cloth  in  it  for  a  few  minutes.  Wash  the 
cloth  in  water  and  note  what  effect  the  acid  has  on  the  strength  of  the 
fiber. 

Ex.  277.  Cover  a  piece  of  cotton  cloth  with  a  30  per  cent  solution  of 
sodium  hydroxide  for  10  or  15  minutes.  Wash  the  cotton  in  water, 
dip  it  in  vinegar,  and  wash  it  again.  Compare  with  the  untreated 
cotton.  How  did  the  sodium  hydroxide  affect  its  strength?  Com- 
pare this  with  the  effect  of  the  acid  in  Ex.  276. 

Ex.  278.  Stretch  a  small  piece  of  white  cotton  cloth  on  a  frame 
and  dip  it  in  a  30  per  cent  solution  of  sodium  hydroxide  for  15  minutes. 
Wash  it  thoroughly  and  note  the  effect  of  the  treatment  on  the  strength 
and  luster  of  the  cotton.  Why  was  the  cloth  stretched  on  a  frame? 
What  is  cotton  treated  in  this  way  called  ? 

Ex.  279.  Examine  fibers  of  linen  under  the  microscope.  Note  the 
absence  of  twist  and  the  presence  of  "knots"  at  the  junction  of  the 


398  APPLIED   CHEMISTRY 

cells.  What  is  the  source  of  linen  ?  What  is  meant  by  retting  the  flax  ? 
How  does  the  strength  of  linen  compare  with  cotton  ?  Which  is  more 
resistant  to  alkalies  and  chlorine  ? 

Ex.  280.  Burn  some  woolen  cloth  and  note  the  odor.  Place  bits  of 
woolen  cloth  in  a  test  tube  and  heat.  Hold  a  piece  of  moist  red  litmus 
paper  in  the  escaping  vapor.  Result?  Hold  a  piece  of  lead  acetate 
paper  in  the  vapor.  Result?  Does  wool  contain  nitrogen  and  sul- 
phur ?  What  are  the  sources  of  wool  for  cloth  making  ? 

Ex.  281.  Examine  fiber  of  wool  under  the  microscope.  Note  the 
saw-tooth  appearance.  Of  what  advantage  is  this  structure  ?  What  is 
meant  by  shoddy  ?  Is  shoddy  as  strong  as  the  original  woolen  cloth  ? 

Ex.  282.  Boil  a  piece  of  pure  woolen  cloth  and  a  piece  of  mixed 
wool  and  cotton  in  a  10  per  cent  solution  of  sodium  hydroxide.  What 
happens  ?  How  is  it  possible  to  distinguish  between  pure  woolen  goods 
and  mixed  goods  ?  Try  the  experiment  on  goods  from  home. 

Ex.  283.  Examine  fibers  of  silk  under  the  microscope  and  compare 
with  wool.  Heat  some  bits  of  silk  in  a  test  tube  and  test  for  ammonia 
and  sulphur.  Results  ?  Compare  with  wool. 

Ex.  284.  Dip  a  piece  of  cotton  cloth  in  a  solution  of  alum.  After 
a  few  minutes  take  out  the  cotton,  wring  it  out  and  dip  it  in  a  dilute 
solution  of  ammonia  water.  Now  dip  this  piece  of  cloth  and  an  un- 
treated piece  into  a  solution  of  logwood  and  boil  it.  After  a  few  min- 
utes withdraw  the  two  pieces  of  cloth  and  wash  them  thoroughly  in 
clear  water.  Is  there  any  difference  in  the  two  pieces  ?  Which  holds 
the  color  better  ?  How  do  you  explain  this  ?  What  is  meant  by  a 
mordant?  (Note.  If  logwood  is  not  available  a  strong  solution  of 
litmus  may  be  substituted  with  fairly  good  results.) 

Ex.  285.  Dip  pieces  of  colored  cotton  cloth  in  a  dilute  solution  of 
bleaching  powder.  Transfer  from  this  solution  to  a  dilute  solution  of 
hydrochloric  acid.  Note  the  effect  on  the  color.  Should  bleaching 
powder  be  used  for  wools  or  silks  ?  How  are  wools  and  silks  usually 
bleached? 


CHAPTER  XLVII 
PAINTS   AND    VARNISHES 

447.  ALL  paints  consist  of  two  parts  :  (1)  an  opaque  solid, 
and  (2)  a  liquid  that  holds  the  solid  in  suspension  while  the 
paint  is  being  spread  on  a  surface,  and  which  causes  it  to 
adhere  firmly  to  the  substance  that  it  covers.     The  solid  is 
called  the  pigment,  and  the  liquid  the  vehicle. 

448.  Linseed  Oil  the  Best  Vehicle.     The  most  commonly 
used  and  the  best  vehicle  for  paint  making  is  linseed  oil, 
which  is  made  from  flaxseed.     The  oil  is  extracted  by  press- 
ing the  ground  seed.     If  the  oil  is  extracted  in  the  cold,  it 
is  very   light   colored,   but   a  more   abundant   yield  of  a 
darker  colored  oil  is  obtained  if  the  seeds  are  subjected  to  heat 
while  being  pressed.     Linseed  oil,  as  has  been  shown  (302), 
absorbs  oxygen  from  the  air  and  is  changed  into  a  tough, 
solid  substance.     This  change  takes  place  readily  when  the 
oil  is  spread  in  a  very  thin  layer.     This  property  of  linseed 
oil  causes  it  and  the  pigment  to  adhere  closely  to  the  surface 
to  which  the  paint  is  applied.      The  pigment  fills  the  pores 
that  form  in  the  film  of  oil  and  helps  to  cover  the  surface 
more  completely  than  would  be  done  by  the  oil  alone. 

449.  Boiled  Oil  and  Driers.     Linseed  oil  that  has  been 
heated  with  lead  oxide  or  the  oxides  of  manganese  will  dry 
more  quickly  than  the  raw  oil.     Such  oil  is  called  boiled  oil. 
The  more  rapid  drying  is  probably  due  to  the  catalytic  action 
of  the  oxides  absorbed  by  the  oil  in  the  process  of  boiling. 
The  paint  can  also  be  made  to  dry  more  quickly  by  adding 
small  quantities  of  so-called  driers.     These  are  substances 
that  absorb  oxygen  from  the  air  and  then  give  it  off  to  the 
oil,  thus  hastening  the  oxidation  or  drying  of  the  oil  itself. 

399 


400  APPLIED   CHEMISTRY 

Turpentine  is  a  substance  of  this  kind,  and  is  commonly 
added  to  paint  when  quick  drying  is  desired. 

Japan  driers  are  made  by  boiling  a  little  oil  with  a  large 
amount  of  lead  or  manganese  oxides,  and  dissolving  the  mix- 
ture in  turpentine.  By  adding  a  small  quantity  of  this  drier 
to  the  paint  it  is  made  to  dry  more  rapidly.  Too  much  drier 
is  objectionable  as  any  such  substance  really  tends  to  make 
the  paint  less  durable.  Much  of  what  is  sold  as  boiled  oil 
is  merely  raw  linseed  oil  to  which  drier  has  been  added. 

450.  Adulterated  Linseed  Oil.     The  comparatively  high 
price  of  linseed  oil  has  led  to  its  frequent  adulteration.     Such 
materials  as  cottonseed  oil  or  corn  oil  are  substituted  in  part 
or  in  whole  for  the  linseed  oil.     These  substitutes  are  not 
drying  oils,  and  paints  made  with  them  will  not  dry.     As  a 
consequence  such  paints  are  not  durable,  especially  when 
exposed  to  the  weather.    Paints  that  remain  sticky  long  after 
application  have  been  mixed  with  other  than  linseed  oil. 
The  best  test  is  to  brush  a  thin  layer  on  a  pane  of  glass 
and  place  it  outdoors  for  forty-eight  hours.     If  the  oil  has 
not  dried  to  a  hard  film  with  no  stickiness,  it  is  not  true 
linseed  oil,  and  is  not  suitable  for  use  in  mixing  paints. 

451.  Common  Pigments.   Those  used  to  form  the  body  of 
paints  are  white  lead  (250)  and  zinc  oxide  (219).    White  lead 
is  the  oldest  of  the  white  pigments  and  is  still  probably  used 
more  than  any  other.     It  has  good  covering  quality  but  has 
the  fault  that  it  rubs  off  or  chalks  after  a   time.     It   also 
darkens  with  age  because  of  the  formation  of  lead  sulphide. 

Zinc  oxide  does  not  cover  so  well  as  white  lead  but  is  more 
durable  and  does  not  chalk  or  darken  with  age.  Probably 
the  best  white  pigment  is  a  mixture  of  white  lead  and  zinc 
oxide,  which  combines  to  a  large  extent  the  covering  power 
of  the  white  lead  and  the  durability  of  the  zinc  oxide.  The 


PAINTS  AND  VARNISHES  401 

highest  grades  of  mixed  paints  are  made  from  white  lead,  zinc 
oxide,  and  pure  linseed  oil.  Many  substances  are  added  to 
both  lead  and  zinc  paints  as  adulterants;  such  as  chalk, 
barites,  lead  sulphate,  kaolin,  and  a  mixture  of  zinc  sulphide 
and  barites  known  as  lithophone.  High-grade  paints  should 
be  free  from  such  adulterants  and  from  benzine  or  gasoline. 

452.  Colored  Paints.     These  are  made  by  adding  some 
colored  pigment  to  the  mixture  of  white  lead  and  zinc  oxide. 
Some  of  the  more  common  are  yellow  ocher  and  red  ocher, 
which  are  oxides  of  iron  and  are  comparatively  inexpen- 
sive;  chrome  yellow,  which  is  lead  chromate;   vermilion, 
a  sulphide  of  mercury ;  Prussian  blue ;  Paris  green ;  chrome 
green,  and  so  on.     Shades  of  gray  are  produced  by  adding 
small  quantities  of  lampblack  to  white  paint. 

453.  Water  Paints.     These  consist  of  a  pigment  suspended 
in  water  and  held  in  place  by  some  cementing  substance  such 
as  glue  or  casein.     These  paints  dry  by  evaporation.     Most 
of  the  water  paints  are  unsuited  to  outside  work,  although 
some  of  those  made  with  casein  have  a  fair  degree  of  per- 
manency when  so  used.     Most  of  the  kalsomines  consist  of 
chalk  and  some  tinting  pigment  suspended  in  a  thin  solution 
of  glue.     Some  of  them,  however,  contain  plaster  of  Paris, 
which  forms  a  hard  coating  as  it  dries. 

Whitewash  is  slaked  lime  mixed  with  water.  When  the 
mixture  is  spread  on  a  surface  the  lime  absorbs  carbon  dioxide 
from  the  air  and  forms  calcium  carbonate.  Ordinary  white- 
wash lasts  only  a  short  time  when  exposed  to  the  weather. 
The  preparation  which  is  given  below,  known  as  Government 
whitewash,  is  fairly  durable  even  for  outdoor  work. 

454.  Government  Whitewash.     Slake  half  a  bushel  of 
lime  in  warm  water  and  cover  it  during  the  process  to  keep 
in  the  steam.     Strain  the  liquid  through  a  fine  sieve  or 

EV.  CHEM.  —  26 


402  APPLIED   CHEMISTRY 

strainer.  Add  a  peck  of  salt  previously  dissolved  in  warm 
water,  three  pounds  of  ground  rice  boiled  to  a  thin  paste  and 
stirred  in  boiling  hot,  a  half-pound  of  powdered  Spanish 
whiting,  and  a  pound  of  glue  which  has  been  previously  dis- 
solved over  a  slow  fire.  Then  add  five  gallons  of  hot  water, 
stir  well,  and  let  it  stand  for  a  few  days  protected  from 
dust  and  dirt.  It  should  be  put  on  hot  with  small  brushes. 
One  pint  of  the  mixture  will  cover  a  square  yard. 

455.  Varnishes  are  used  to  provide  protecting  coats  that 
are  transparent  and  reveal  the  grain  of  the  wood.     As  with 
mixed  paints,  there  is  a  great  variation  in  the  quality  of  the 
varnishes  on  the  market.     A  good  varnish  should  stand 
water,  and  should  not  "  dust"  when  scratched.     Two  general 
types  of  varnishes  are  oil  varnishes  and  spirit  varnishes. 

The  oil  varnishes  are  made  by  melting  a  resin  or  gum  and 
dissolving  it  in  hot  linseed  oil,  and  then  thinning  the  mixture 
to  the  proper  consistency  with  turpentine.  When  made  from 
pure  linseed  oil  and  a  good  gum  such  as  opal,  amber,  or 
dammar,  a  varnish  is  produced  that  gives  a  tough,  water- 
resisting  film.  Cheaper  furniture  varnishes,  consisting  of 
common  rosin  dissolved  in  oil,  lack  wearing  quality. 

Spirit  varnishes  are  made  by  dissolving  gums  or  resins  in 
denatured  alcohol  or  wood  alcohol.  These  dry  by  simple 
evaporation  of  the  solvent,  and  the  gum  is  left  unchanged 
except  that  it  has  been  spread  out  in  a  thin  film.  The  most 
common  varnish  of  this  kind  is  the  well-known  shellac. 
Spirit  varnishes  are  not  so  durable  as  the  oil  varnishes. 

456.  Enamel  Paints.     These  are  made  by  grinding  pig- 
ments in  a  good  varnish  instead  of  in  linseed  oil.     The  best 
white  enamel  paints  consist  of  zinc  oxide  ground  in  a  dammar 
varnish.     Many  of  the  enamel  paints,  however,  are  made 
from  cheap  varnishes  and  inferior  pigments  and  fillers. 


PAINTS  AND  VARNISHES  403 

457.  Black  Varnishes.  Varnishes  used  for  coating  iron  are 
prepared  by  dissolving  coal  tar,  pitch,  or  asphaltum  in  tur- 
pentine or  benzine.  They  give  excellent  protecting  surfaces 
where  the  black  color  is  not  objectionable.  A  very  thin 
solution  of  these  materials  in  benzine  is  often  used  as  a  stain 
for  wood.  The  creosote  stain  often  used  on  shingles  is  a 
coal-tar  product,  which  preserves  as  well  as  stains  the  wood. 

EXERCISES 

Ex.  286.  What  is  meant  by  the  pigment  in  paints  ?  By  the  vehi- 
cle? What  is  the  best  vehicle?  How  is  linseed  oil  prepared?  What 
happens  to  it  when  exposed  to  the  air  ?  What  is  meant  by  boiled  oil  ? 
Why  is  the  oil  so  prepared  ?  What  is  meant  by  a  drier  and  how  does  it 
act  ?  Why  is  turpentine  used  in  paints  ?  What  is  Japan  drier  ? 

Ex.  287.  Obtain  a  sample  of  linseed  oil  (from  home  if  possible)  and 
brush  a  little  out  into  a  very  thin  layer  on  a  pane  of  glass.  Examine 
this  at  the  end  of  24  hours  and  48  hours.  Does  the  oil  harden  com- 
pletely ?  Is  it  suitable  for  paint  making  ? 

Ex.  288.  What  are  the  two  best  pigments  for  paint  making  ?  State 
advantages  of  each.  Why  is  a  mixture  of  both  most  desirable  ?  How 
are  colored  paints  made  ? 

Ex.  289.  Test  a  sample  of  paint  from  home  for  purity  of  the  pig- 
ments as  follows:  (1)  Remove  all  the  oil  from  a  tablespoonful  of  the 
solid  sediment  of  the  paint,  by  washing  it  several  times  by  decantation 
with  gasoline.  Spread  the  residue  out  to  dry.  (2)  Boil  a  portion  of 
the  dry  material  with  strong  acetic  acid.  A  residue  indicates  barites 
or  other  adulterants.  (3)  Test  another  portion  on  charcoal  for  lead 
according  to  paragraph  252.  (4)  Test  another  portion  for  zinc  accord- 
ing to  paragraph  221.  Record  the  results  of  your  test. 

Ex.  290.  Of  what  do  water  paints  consist?  What  is  whitewash? 
Are  water  paints  usually  durable  for  outside  work  ?  Try  the  Govern- 
ment whitewash  any  place  about  the  home  where  whitewash  is  used. 

Ex.291.  How  are  varnishes  made  ?  What  are  the  characteristics  of 
a  good  varnish  ?  What  are  spirit  varnishes  ?  Compare  the  finish  from 
the  two  kinds  of  varnish.  How  are  enamel  paints  made  ?  What  is  the 
black  varnish  that  is  often  used  in  coating  iron  ? 


CHAPTER  XLVIII 
CLEANING   MATERIALS 

458.  THE  operations  of  cleaning  involve  both  physical  and 
chemical  processes.     Dirt  can  sometimes  be  removed  by 
means  of  brushing,  shaking,  or  simple  agitation  under  water. 
The  dirt  is  first  loosened  by  friction  and  then  carried  away  by 
currents  of  air  or  water.     It  is  usually  held  in  place,  how- 
ever, by  particles  of  grease  or  some  sugary  or  gummy  ma- 
terial and  cannot  be  removed  by  strictly  mechanical  means. 
Sugary  spots  may  be  removed  by  warm  water  alone,  but 
when  the  dirt  is  held  by  a  film  of  grease,  some  substance 
must  be  used  that  will  remove  the  grease.      Soap  is  ordi- 
narily employed  to  accomplish  this  end. 

459.  Soaps.     It  has  been  explained  (303)  that  soaps  are 
the  sodium  or  potassium  salts  of  the  fatty  acids,  and  are 
made  by  boiling  fats  or  oils  with  the  carbonates  or  hydroxides 
of  sodium  or  potassium.     Most  of  the  soaps  on  the  market 
are  sodium 'soaps  and  belong  to  the  class  known  as  hard 
soaps.     Soft  soaps  are  made  with  potassium  compounds  but 
are  not  commonly  found  on  the  market.     About  the  only 
familiar  example  of  soft  soap  is  the  old-fashioned  homemade 
soap  which  is  manufactured  from  waste  fats  and  lye. 

The  cleaning  power  of  soap  is  to  some  extent  due  to  the 
fact  that  it  partially  dissociates  when  dissolved  in  water, 
liberating  a  little  free  alkali  which  acts  upon  the  grease  to  be 
removed.  Probably  its  most  important  action  is  its  power 
to  emulsify  the  grease  of  the  dirt  spot.  Dirt  and  small 

404 


CLEANING  MATERIALS  405 

particles  of  the  emulsified  fat   become  thoroughly  mixed 
with  the  suds,  and  upon  rinsing  are  removed  with  the  soap. 

460.  Pure  Soap.     Such  a  soap  should  contain  no  excess 
of  alkali  or  of  unchanged  fat.     A  good  test  for  free  alkali  is 
made  by  dropping  a  little  phenolphthalein  indicator  on  the 
freshly  cut  surface  of  a  bar  of  soap.     A  coloration  of  the 
indicator  shows  the  presence  of  free  alkali.     Unsaponified 
fat  can  be  determined  by  drying  a  portion  of  the  soap  in 
the  oven  and  then  extracting  the  dry  material  with  gasoline. 
If  the  gasoline  leaves  a  greasy  film  upon  evaporation,  the 
presence  of  unchanged  fat  is  indicated. 

Toilet  soaps  especially  should  contain  no  free  alkali,  as  the 
latter  is  injurious  to  the  skin.  Even  in  laundry  soaps  any 
large  amount  of  free  alkali  is  objectionable  if  the  soaps  are  to 
be  used  for  washing  woolen  or  silk  goods  or  any  kind  of 
colored  material.  Strong  perfumes  are  so  often  used  to 
cover  the  odor  of  the  lye  and  other  objectionable  materials 
that  it  is  advisable  in  general  to  avoid  all  highly  scented  soaps. 

461.  Hard  Water  Wastes  Soap.      When  soap  is  used  in 
hard  water  a  scum  appears  on  the  surface  of  the  water. 
This  is  due  to  the  fact  that  the  calcium  and  magnesium  salts 
in  the  hard  water  react  with  the  soap,  forming  calcium  and 
magnesium  salts  of  the  fatty  acids  of  the  soap.     These 
calcium  and  magnesium  salts  are  insoluble  in  water  and  are 
so  light  that  they  float.     As  these  salts  are  insoluble  they 
have  no  emulsifying  or  cleaning  power;  hence   the  amount 
of  soap  that  reacts  with  calcium  and  magnesium  is  wasted. 
Soap  does  not  begin  to  lather  until  all  the  lime  and  mag- 
nesia have  been  removed  from  the  water.     In  this  case  soap 
itself  softens  the  water  before  it  begins  the  real  cleaning 
process ;  but  it  is  an  expensive  method  of  softening  water. 

462.  Foreign  Ingredients  in  Soaps.    Many  of  the  soaps 


406  APPLIED   CHEMISTRY 

found  on  the  market  are  adulterated.  Washing  soda,  or 
sodium  carbonate,  in  excessive  quantities  is  present  in  many 
laundry  soaps.  The  soaps  especially  recommended  for  hard 
water  usually  contain  a  large  amount  of  sodium  carbonate. 
While  such  a  soap  may  not  be  objectionable  for  use  on  cotton 
goods  in  hard  water,  washing  soda  bought  in  this  way  is  very 
expensive.  Another  common  adulterant  of  laundry  soap  is 
sodium  silicate,  or  water  glass.  This  substance  has  some 
cleansing  power,  but  its  use  results  in  an  inferior  soap.  A 
few  soaps  contain  a  small  percentage  of  borax. 

Common  rosin  when  boiled  with  an  alkali  forms  a  sub- 
stance resembling  soap.  The  yellow  laundry  soaps  are 
usually  made  from  a  mixture  of  rosin  and  fats  and  are  in- 
ferior to  soaps  made  wholly  from  fats.  Rosin  soaps  are 
not  particularly  objectionable  for  washing  cotton  goods,  but 
with  woolens  they  are  likely  to  deposit  rosin  in  the  fiber  and 
make  the  goods  harsh  to  the  touch. 

Some  soaps  for  use  in  cold  water  contain  naphtha  or 
kerosene.  These  substances  are  added  for  the  specific 
purpose  of  assisting  in  dissolving  the  grease  so  that  heat  will 
not  be  necessary,  and  are  not,  therefore,  to  be  considered 
as  adulterants.  Soaps  are  also  frequently  adulterated  with 
substances  of  no  cleaning  value  called  fillers,  which  are 
added  solejy  to  increase  the  weight  of  the  soap.  Sodium 
sulphate,  gypsum,  whiting,  chalk,  and  almost  anything  else 
that  is  cheap  and  bulky  are  used  as  fillers. 

Water  in  excess  of  25  per  cent  is  also  considered  an  adulter- 
ant. Too  much  water  makes  the  soap  soft  so  that  it  dis- 
solves rapidly.  A  dry  soap  does  not  waste  so  readily; 
hence  it  is  economy  to  buy  laundry  soap  in  quantities, 
unwrap  the  bars,  and  pile  them  loosely,  so  that  the  soap  can 
dry  as  thoroughly  as  possible  before  being  used. 


CLEANING  MATERIALS  407 

463.  Washing   Soda   and   Other  Alkalies.     Where   hard 
water  must  be  employed,  a  judicious  use  of  sodium  carbonate 
results  in  a  saving  of  soap.     Just  enough  soda  should  be 
added  to  precipitate  the  lime  and  magnesia  in  the  water. 
The  soda  should  first  be  dissolved  in  a  small  quantity  of 
water  and  this  solution  should  be  gradually  added  to  the  laun- 
dry water,  care  being  taken  to  avoid  any  great  excess.    Caus- 
tic soda  (soda  lye)  is  sometimes  used  for  the  same  purpose ; 
but  its  use  requires  more  care  than  ordinary  washing  soda. 
The  use  of  either  substance  with  silk  or  woolen  goods  is  at- 
tended with  risk,  and  colored  goods  of  all  kinds  are  likely  to 
be  injured  by  a  slight  excess  of  alkali  in  the  wash  water. 
Borax  is  occasionally  used  when  a  milder  alkali  than  washing 
soda  is  needed,  but  it  is  much  more  expensive  than  soda. 

Ammonia  water  is  also  used  to  soften  hard  water.  It  is 
the  safest  alkali  to  use  in  many  cases  because  it  evapo- 
rates very  rapidly  and  does  not  remain  in  contact  with  the 
goods  long  enough  to  injure  the  fiber.  The  alkalies  will 
destroy  any  materials  made  from  oils  or  resins,  hence 
strongly  alkaline  solutions  should  never  be  used  on  paints 
or  varnishes. 

464.  Soap  Powders  and  Scouring  Soaps.     Many  of  the 
washing  powders  on  the  market  are  nothing  but  washing 
soda.     Others  contain  a  small  percentage  of  soap  shavings 
mixed  with  a  large  amount  of  soda.     It  is  probably  more 
economical  to  buy  the  washing  soda  ahd  soap  separately 
than  to  purchase  them  in  the  form  of  washing  powders. 

Scouring  soaps  and  powders  consist  for  the  most  part  of  a 
small  amount  of  soap  mixed  with  washing  soda  and  some 
scouring  powder,  such  as  whiting,  chalk,  powdered  pumice, 
fine  sand,  or  infusorial  earth.  The  scouring  material  should 
not  be  so  coarse  as  to  scratch  the  article  to  be  cleaned. 


408 


APPLIED   CHEMISTRY 


465.  Solvents  for  Fats.  When  a  grease  spot  occurs  in  a 
fabric  which  for  any  reason  cannot  be  washed,  it  is  necessary 
to  use  some  substances  that  will  dissolve  the  grease  and  carry  it 
away.  The  most  commonly  used  materials  are  gasoline  and 
benzine.  These  liquids  dissolve  all  the  fats  and  are  largely 
used  in  what  is  known  as  the  dry-cleaning  process.  To  get 
the  best  results  some  absorbing  material  must  be  placed 
beneath  the  fabric  to  be  cleaned  so  that  the  grease  can  be 
washed  through  by  the  gasoline  or  other  solvent.  To  add  a 
little  gasoline  and  rub  the  spot,  merely  spreads  the  grease  into 
a  larger  and  thinner  film.  Sometimes  the  goods  are  rinsed 

in  several  changes  of 
gasoline  to  remove  the 
grease. 

Ordinary  ether  is 
even  better  than  gaso- 
line for  removing  fats ; 
but  its  high  cost  pre- 
vents its  use  except  for 
certain  special  pur- 
poses. All  the  solvents 
ordinarily  used  for  re- 
moving grease  from 
clothing  are  highly  in- 
flammable, and  their 
vapors  make  explosive 
mixtures  with  air.  Great  care  should  be  exercised  in  using 
any  of  these  materials,  and  they  should  never  be  used  in  a 
room  in  which  there  is  a  fire.  Whenever  possible  the  cleaning 
should  be  done  out  of  doors. 

A  comparatively-  new  substance  known  as  carbon  tet- 
rachloride  (CClj)  is  sometimes  used  to  remove  grease 


FIG.  182.  —  Cleaning  clothing  with  gasoline. 


CLEANING  MATERIALS  409 

from  fabrics.  It  has  the  advantage  of  not  being  in- 
flammable. 

Both  gasoline  and  kerosene  dissolve  the  calcium  and 
magnesium  soaps.  Probably  for  this  reason  it  is  advan- 
tageous to  place  a  little  kerosene  in  the  boiler  in  which  cloth- 
ing is  boiled.  For  the  same  reason  either  substance  is  useful 
in  cleaning  bath  tubs  and  basins  where  hard  water  is  used. 

466.  Spots  and  Stains.  These  come  from  such  a  variety 
of  causes  that  no  remedy  can  be  suggested  unless  the  cause 
of  the  stain  is  known.  At  the  best,  however,  it  is  practically 
impossible  to  remove  stains  from  delicately  colored  fabrics 
without  destroying  the  color  of  the  dye  as  well. 

Fruit  juices  and  other  acid  substances  frequently  discolor 
dyed  materials,  especially  the  blues.  The  color  can  some- 
times be  restored  by  weak  ammonia  water  if  applied  in  time. 
Many  fruit  stains  can  be  removed  by  hot  water  when  fresh 
but  are  resistant  to  treatment  when  old. 

Alcohol  will  remove  grass  stains  (chlorophyll),  and  spots 
of  varnish,  and  some  paints.  Consequently  care  should 
be  exercised  to  avoid  spilling  alcohol,  perfume,  or  other 
substance  containing  alcohol  on  any  varnish  finished 
surface. 

Ink  was  formerly  always  made  from  iron  tannate.  This 
compound  is  soluble  in  weak  acids,  and  can  be  removed, 
when  not  too  old,  by  lemon  juice  and  salt,  oxalic  acid,  or 
even  very  dilute  hydrochloric  acid.  The  acid  substance 
should  be  added  cautiously  and  the  material  should  be  washed 
as  soon  as  the  color  of  the  ink  spot  disappears.  Many  of  the 
inks  now  on  the  market  are  made  from  aniline  dyes  and  are 
not  affected  by  the  weak  acids.  For  them  there  is  no  method 
of  removal  that  will  not  affect  the  dye  of  the  cloth  as  welL 
White  goods  can  often  be  bleached  to  remove  such  ink  spots. 


410  APPLIED   CHEMISTRY 

EXERCISES 

Ex.  292.  Review  Exercises  176  and  177.  What  is  the  chemical 
composition  of  a  soap  ?  How  do  soaps  clean  ? 

Ex.  293.  Test  several  samples  of  both  white  and  yellow  soaps  for 
free  alkali  by  putting  a  drop  of  phenolphthalein  indicator  on  the  freshly 
cut  surface  of  the  soaps.  Which  show  free  alkali  ?  Would  they  make 
good  toilet  soaps  ?  Were  any  of  the  soaps  especially  recommended  for 
hard  water  ?  Why  should  strongly  perfumed  soaps  be  avoided  ? 

Ex.  294.  Do  you  use  hard  or  soft  water  at  home  for  washing  ?  Ex- 
plain how  hard  water  wastes  soap.  What  is  the  curd  that  floats  on  the 
top  of  hard  water  when  soap  is  used  in  it  ? 

Ex.  295.  Name  some  of  the  foreign  ingredients  sometimes  found  in 
soap.  Why  is  it  objectionable  to  have  large  quantities  of  sodium  car- 
bonate in  soap  ?  Why  is  rosin  objectionable  ?  What  is  meant  by  fillers 
in  soap  ?  What  are  naphtha  soaps  ? 

Ex.  296.  Dissolve  a  small  piece  of  scouring  soap  in  hot  water. 
What  is  the  nature  of  the  residue  ?  On  a  sample  of  any  washing  pow- 
der pour  a  little  hydrochloric  acid.  Is  sodium  carbonate  present  ? 

Ex.  297.  Explain  the  softening  action  of  sodium  carbonate  on  hard 
water.  Why  should  it  be  used  cautiously  with  silks  and  wools  ?  What 
advantage  has  ammonia  water  for  use  on  woolens  ?  Why  should  strong 
alkalies  be  avoided  on  paints  and  varnishes? 

Ex.  298.  What  kinds  of  spots  can  be  removed  by  gasoline  or  ether  ? 
Upon  what  does  their  action  depend  ?  How  are  the  best  results  ob- 
tained? What  precautions  are  necessary  in  using  gasoline  or  ether? 

Ex.  299.  Make  various  spots  on  cotton  or  woolen  goods,  or  use 
clothing  already  spotted,  and  attempt  to  remove  the  spots  by  the  various 
methods  mentioned  in  this  chapter. 


CHAPTER  XLIX 


INSECTICIDES  AND   FUNGICIDES 

467.  Losses  due  to  Insects.  It  has  been  estimated  that 
ten  per  cent  of  the  value  of  farm  crops  is  lost  through  the 
destruction  caused  by  injurious  insects,  and  that  this  loss 
amounts  to  four  times 
that  due  to  all  destruc- 
tion of  property  by  fire. 
The  farmer  and  the  gar- 
dener, therefore,  are  in- 
terested in  the  .methods 
of  controlling  injurious 
insects.  These  insects 
are  divided  into  two 
general  classes :  those 
that  eat  the  tissues  of 
the  plant,  and  those 
that  suck  out  the  plant 
juices  and  so  injure  the 
plant.  Insects  that  bite 
may  be  killed  by  cover- 
ing the  plant  with  a 
so-called  stomachic 
poison,  which  the  insect 
swallows.  The  insects  FlG'  183'  ~" Spraying  trees> 

which  merely  suck  the  sap  cannot  be  killed  by  the  stomachic 
poison  but  are  destroyed  by  contact  poisons,  which  cause 
death  by  their  caustic  action  on  the  body  of  the  insect. 

411 


412  APPLIED   CHEMISTRY 

468.  Stomachic  Poisons.     These  poisons  usually  contain 
arsenic  in  some  form.   The  oldest  of  these  is  Paris  green  (260), 
which  is  a  compound  of  copper  with  arsenious  acid  and 
acetic  acid.     From  one  half  to  one  pound  of  Paris  green  is 
used  to  fifty  gallons  of  water.     Paris  green  even  in  this 
dilute  solution  will  sometimes  scorch  the  leaves,  and  to  pre- 
vent this  action  two  pounds  of  slaked  lime  are  added. 

Ar senate  of  lead  (251)  is  rapidly  replacing  Paris  green  as 
an  insecticide.  It  is  purchased  either  in  the  form  of  a  paste 
or  a  powder  and  is  used  at  the  rate  of  from  2  to  4  pounds  in 
50  gallons  of  water.  It  is  more  adhesive  than  Paris  green 
and  does  not  injure  the  foliage. 

Powdered  hellebore  is  used  to  a  limited  extent  by  garden- 
ers, especially  for  ornamental  plants.  The  powder  is  mixed 
with  hot  water  and  then  diluted  and  sprayed  on  the  plants. 

469.  Contact   Poisons.     The  first   used   of   the   contact 
poisons  was  kerosene  emulsion.     The  kerosene  is  vigorously 
agitated  with  soapsuds  until  a  jellylike  emulsion  is  formed 
which  can  then  be  diluted  with  water  without  separating. 
It  kills  the  insect  by  inclosing  its  body  with  a  film  of  oil.     If 
properly  made,  the  emulsion  is  not  injurious  to  the  foliage. 

470.  Lime  sulphur  is  probably  used  more  than  any  other 
contact  poison.     Some  of  the  insects,  the  San  Jose  scale  for 
example,  have  the  power  of  covering  their  bodies  with  a 
protecting    scale    and    consequently    a    penetrating    spray 
mixture  is  necessary  to  reach  them.     Lime-sulphur  mixture 
seems  to  give  the  best  results  with  these  insects.     It  is  made 
by  boiling  together  lime  and  flowers  of  sulphur.     The  lime 
and  sulphur  unite  to  form  the  polysulphides  of  calcium, 
probably  largely  CaS4  and  CaS5.     When  exposed  to  the  air 
the   polysulphides   decompose,    setting   free   sulphur.     The 
insecticidal  action  of  this  spraying  mixture  is  due  partly  to 


INSECTICIDES  AND  FUNGICIDES  413 

its  caustic  action  on  the  insect,  and  partly  to  the  poisonous 
effect  of  the  nascent  sulphur  which  is  liberated.  Lime- 
sulphur  solution  is  now  made  commercially  on  a  large  scale 
and  is  not  so  generally  manufactured  on  the  farm  as  formerly. 
To  kill  the  scale  a  strong  solution  is  used  when  the  trees  are 
dormant.  After  the  leaves  appear,  a  weak  solution  is  used 
for  certain  other  insects  and  diseases. 

471.  Whale  Oil  Soap.     This  and  other  soaps  made  from 
fish  oils  are  frequently  used  to  destroy  scale  insects.     The 
soap  is  dissolved  in  boiling  water  at  the  rate  of  two  pounds 
to  the  gallon  of  water  and  is  applied  while  hot.     It  is  used 
principally  for  the  winter  treatment  of  scale-infected  trees. 

Common  laundry  soap  dissolved  in  water  at  the  rate  of 
one  bar  of  soap  to  two  bucketfuls  of  water  makes  an  effective 
contact  insecticide  for  the  small  garden.  A  white  soap  free 
from  rosin  is  to  be  preferred. 

472.  Tobacco  is  sometimes  used  for  the  destruction  of 
insects  on  house  plants.     The  stems  or  other  refuse  parts  of 
the  tobacco  plant  are  steeped  in  water  and  the  solution  is 
sprayed  on  the  plant.     Sometimes  in  place  of  this  decoction 
of  tobacco  a  solution  of  nicotine  sulphate  is  used.  -It  will  be  re- 
membered that  tobacco  contains  an  alkaloid  known  as  nico- 
tine (326).     The  salt  formed  by  this  alkaloid  and  sulphuric 
acid  is  the  basis  of  such  insecticides  as  Black  Leaf-40.     It 
is  used  especially  to  kill  the  aphis  or  plant  louse. 

473.  Pyrethrum  Powder.     This  powder,  also  known  as 
Buhach  and  Persian  insect  powder,  is  composed  of  the  pul- 
verized flower  heads  of  certain  plants  of  the  genus  pyrethrum. 
It  is  a  valuable  insecticide  for  use  in  a  small  way  when  fresh, 
but  soon  loses  its  strength,  especially  if  it  is  exposed  to  the 
air.     It  is  used  by  dusting  it  on  the  plant  or  by  steeping  it 
in  water  and  using  the  resulting  liquid.     The  fumes  of  the 


414  APPLIED   CHEMISTRY 

burning  powder  are  useful  also  in  destroying  insects  in  a 
confined  space. 

474.  Gaseous  Insecticides.     Hydrocyanic  acid   (209)   is 
sometimes  used  as  an  insecticide  in  greenhouses  and  in  the 
orange  groves  of  California.     It  is  used  in  greenhouses  in  the 
following  manner :  the  operator  places  dilute  sulphuric  acid 
in  suitable  vessels  and  then  drops  into  each  vessel  a  quantity 
of  potassium  cyanide  wrapped  in  paper.     He  immediately 
steps  outside  and  closes  the  house  tightly.     After  a  few  hours 
the  house  is  opened  from  the  outside  and  thoroughly  ven- 
tilated before  any  one  ventures  inside.     In  the  orange  groves 
each  tree  is  covered  with  a  tent  for  fumigation  purposes. 
Hydrocyanic  gas  is  a  deadly  poison  and  should  be  handled 
only  by  persons  skilled  in  its  use. 

475.  Carbon  Bisulphide  (110).     This  is  used  for  killing 
weevils  and  other  insects  in  stored  grains.     The  liquid  is 
placed  in  dishes  at  a  number  of  places  on  the  surface  of 
the  grain,  about  a  teaspoonful  being  used  for  each  cubic  foot 
of  space.     The  carbon  bisulphide  vaporizes,  and  the  vapor, 
which  is  heavier  than  air,  settles  down  through  the  grain. 
Carbon  bisulphide  is  used  also  to  exterminate  rodents  (110). 
It  is  inflammable  and  should  not  be  used  near  a  flame. 

476.  Sheep   Dips   and   Fly   Repellents.     The   materials 
used  in  dipping  sheep  for  the  purpose  of  killing  their  insect 
parasites    are  largely  coal-tar  products,   cresol    being    the 
substance  most  commonly  used.      Light  coal-tar  oils  and 
other  coal-tar  products  are  sometimes  sprayed  on  cattle  to 
repel  flies.     These  repellents  should  be  made  of  materials 
which,  when  they  evaporate,  leave  no  sticky  or  gummy  sub- 
stance on  the  hair  of  the  cattle. 

477.  Insecticides    for    the    Household.    The    common 
method  of  control  for  the  common  house  fly  is  by  means  of 


INSECTICIDES  AND  FUNGICIDES  415 

some  kind  of  fly  paper.  The  sticky  fly  papers  are  coated 
with  a  mixture  of  common  rosin  and  castor  oil.  The  ordi- 
nary poison  fly  paper  is  impregnated  with  a  dilute  solution 
of  sodium  arsenite.  Care  should  be  exercised  in  using  it, 
since  children  have  been  known  to  be  poisoned  by  drinking 
the  sweetened  water  in  which  the  paper  is  placed. 

A  two  per  cent  solution  of  formaldehyde  (a  teaspoonful 
of  formalin  to  a  cupful  of  water)  is  said  to  be  as  effective  in 
killing  flies  as  the  poison  paper  and  has  the  advantage  of  not 
being  poisonous  to  human  beings.  A  little  honey  or  milk  is 
added  to  the  solution  to  attract  the  flies.  If  many  flies  are 
present,  they  may  be  killed  by  burning  pyrethrum  powder 
in  the  tightly  closed  room. 

The  favorite  breeding  places  of  flies  are  the  garbage  can, 
the  manure  pile,  and  other  places  where  decomposing  or- 
ganic matter  is  found.  Such  materials  should, when  possible, 
be  so  handled  as  to  prevent  the  flies  from  having  access  to 
them.  It  is  said  that  hellebore,  borax,  or  acid  phosphate 
scattered  on  manure  piles  prevents  the  breeding  of  flies. 

Sodium  fluoride,  NaF,  is  recommended  for  the  extermina- 
tion of  cockroaches  and  red  ants.  It  is  scattered  over  the 
tables,  sinks,  or  pantry  shelves  where  these  insects  are  found. 

No  insects  cause  the  housewife  more  worry  than  the 
clothes  moth  which  is  so  destructive  to  woolens  and  furs 
especially.  The  moth  balls  so  commonly  used  consist  of 
naphthalene  (Ci0H8),  a  substance  prep'ared  from  coal  tar. 
It  repels  the  moth  and  prevents  it  from  laying  the  eggs  on 
the  clothing.  If  the  eggs  have  already  been  deposited,  the 
naphthalene  has  no  value.  The  caterpillar  which  hatches 
from  the  eggs  and  does  the  real  damage  may  be  destroyed 
by  dusting  the  garment  heavily  with  pyrethrum  powder. 
Sometimes  the  infected  clothing  is  placed  in  a  tight  box  and 


416  APPLIED  CHEMISTRY 

treated  with  carbon  bisulphide  as  described  for  the  treat- 
ment of  grains  (475).  In  the  cities  furs  are  sometimes 
placed  in  cold  storage  during  the  summer  at  a  temperature 
so  low  that  the  eggs  cannot  hatch. 

The  common  bedbug  is  destroyed  by  applying  gasoline 
freely  to  every  crack  and  crevice  in  which  it  is  possible  for 
the  bug  to  hide.  Repeated  treatments  of  this  kind  will 
effectively  control  this  pest.  Fleas  on  dogs  and  other  ani- 
mals may  be  exterminated  by  the  free  use  of  pyrethrum 
powder.  This  powder  is  not  poisonous  to  the  higher  animals, 
and  its  use,  therefore,  is  attended  with  no  danger. 

Old  houses  occasionally  become  so  overrun  with  insect 
pests  that  all  ordinary  methods  fail.  In  such  cases  a  resort 
to  fumigation  with  hydrocyanic  acid  gas  is  justified.  The 
same  general  method  as  that  described  for  fumigating  green- 
houses is  used.  This  gas  destroys  all  animal  life  which  is  in 
the  house,  and  is  such  a  deadly  poison  that  the  greatest 
precaution  should  be  observed  in  using  it. 

Fungicides.  Plants  are  often  injured  by  fungi  that  grow 
parasitically  upon  them.  Some  of  these  disease-producing 
fungi  can  be  destroyed  by  spraying  with  a  proper  fungicide. 

478.  Bordeaux  Mixture.     Probably  the  best  known  of  the 
fungicides   is  made  by  mixing  a  solution  of  copper    sul- 
phate with  milk  of  lime  (259)  and  diluting  the  mixture  with 
water.     It  is  the  most  common  spray  used  on  apple  trees. 
As  trees  are  attacked  by  insects  at  the  time  that  they  are 
suffering  from  fungus  diseases,  it  is  customary  to  add  ar- 
senate  of  lead  or  Paris  green  to  the  Bordeaux  mixture  so  as 
to  make  the  one  mixture  both  an  insecticide  and  fungicide. 

479.  Lime  sulphur  has  marked  fungicidal  properties,  and 
a  dilute  solution  of  lime  sulphur  is  used  in  place  of,  or  in 
addition  to,  the  Bordeaux  mixture  for  summer  spraying. 


INSECTICIDES  AND  FUNGICIDES 


417 


Arsenate  of  lead  is  sometimes  mixed  with  the  lime-sulphur 
mixture. 

480.  Formaldehyde,  or  formalin,  is  commonly  used  to 
kill  the  smut  fungus  on  oats  and  other  grains.  The  com- 
mercial 40  per  cent  solution  of  formaldehyde  is  used  at  the 
rate  of  one  pint  to  20  gallons  of  water.  Seeds  are  immersed 
in  this  solution  for  10  minutes  and  then  spread  out  to  dry. 


FIG.  184.  —  Treating  seed  potatoes  with  formalin  to  prevent  scab. 

A  new  method  for  treating  oats  for  smut,  which  avoids  the 
necessity  of  drying  the  seeds,  has  recently  been  reported  by 
the  New  York  State  College  of  Agriculture.  This  method 
in  brief  is  as  follows :  one  pint  of  the  40  per  cent  solution  of 
formaldehyde  is  diluted  with  one  pint  of  water  and  placed  in 
a  quart  hand  sprayer.  The  oats  are  placed  on  a  clean  barn 
floor  or  on  a  tight  wagon  box.  While  the  oats  are  being 
shoveled  from  one  pile  to /another  each  shovelful  is  sprayed 
with  the  solution,  giving  one  movement  of  the  handle  for  each 
shovelful.  After  the  oats  are  all  treated  in  this  way,  they  are 
EV.  CHBM.  —  27 


418  APPLIED  CHEMISTRY 

piled  in  a  heap  and  covered  with  blankets,  canvas,  or  grain 
sacks  which  have  been  sprayed  inside  and  out  with  the 
solution.  They  are  allowed  to  stand  for  at  least  five  hours, 
after  which  they  may  be  bagged  and  drilled.  The  above 
amount  of  solution  is  sufficient  to  treat  50  bushels  of  oats. 

Formaldehyde  is  also  used  in  a  similar  way  to  kill  the  scab 
fungus  on  the  seed  potatoes  (Fig.  184),  as  is  also  a  weak 
solution  of  corrosive  sublimate.  More  or  less  complete 
descriptions  of  all  these  insecticides  and  fungicides  are  pub- 
lished by  many  of  the  state  experiment  stations  and  by  the 
United  States  Department  of  Agriculture. 

481.  Bacterial  Diseases.  The  fungus  diseases  that  are 
readily  affected  by  sprays  are  those  which  grow  on  the  surface 
of  leaves  and  stems.  Many  of  the  diseases  of  plants  are 
caused  by  bacteria  and  are  so  deep-seated  as  to  be  beyond 
the  reach  of  the  spray  materials.  Some  of  these  can  be 
eradicated  by  careful  pruning.  Still  other  diseases  have, 
thus  far,  defied  all  treatments,  and  when  they  appear  the 
tree  must  be  destroyed  to  check  the  spread  of  the  disease. 

EXERCISES 

Ex.  300.  To  what  extent  are  crops  injured  by  insects  ?  Into  what 
two  classes  may  these  insects  be  divided  according  to  their  manner  of 
feeding  ?  What  two  classes  of  poisons  are  necessary  to  destroy  them  ? 
What  is  the  more  common  constituent  of  the  stomachic  poisons  ?  What 
are  the  two  more  important  arsenic  preparations  used  as  insecticides? 
Why  should  lime  always  be  used  with  Paris  green  ? 

Ex.  301.  How  do  contact  poisons  act  ?  How  is  kerosene  emulsion 
made?  What  is  a  good  contact  poison  for  a  small  garden?  What 
tobacco  preparations  are  used  as  insecticides?  What  is  pyrethrum 
powder  and  how  is  it  used  ?  By  what  other  names  is  it  known  ?  What 
methods  can  you  suggest  for  controlling  the  house  fly  ?  How  can  you 
rid  the  house  of  cockroaches  or  ants  ?  How  can  you  protect  clothing 
from  moths  ? 


INSECTICIDES  AND  FUNGICIDES  419 

Ex.  302.  Slake  25  grams  of  lime  and  add  to  200  cc.  of  water.  Add 
50  grams  of  flowers  of  sulphur.  Heat  gradually  to  boiling,  with  constant 
stirring,  and  boil  half  an  hour.  Allow  to  settle  and  decant  the  clear 
liquid.  What  is  the  color  of  the  liquid  ?  What  is  this  substance  called  ? 
Of  what  does  it  probably  consist  ?  To  what  are  its  insecticidal  proper- 
ties due  ?  At  what  season  is  it  used  to  kill  the  scales  ? 

Ex.  303.  Explain  the  use  of  hydrocyanic  acid  as  an  insecticide. 
Why  is  it  so  Dangerous  to  work  with  it  ?  How  is  it  used  in  the  orange 
groves?  Wtyat  is  carbon  bisulphide?  Explain  its  use  to  kill  weevil. 
Review  Ex.  77.  Why  should  carbon  bisulphide  never  be  used  near 
afire? 

Ex.  304.  Dissolve  half  a  pound  of  copper  sulphate  in  a  quart  of  hot 
water.  Slake  half  a  pound  of  lime  in  a  quart  of  water.  Strain  the 
milk  of  the  lime  through  a  cheesecloth.  Pour  the  copper  solution  into 
the  limewater  with  constant  stirring.  What  is  this  mixture  called? 
For  what  is  it  used  ?  Why  should  the  copper  sulphate  solution  never 
be  put  into  an  iron  vessel  ?  Read  the  bulletins  for  a  description  of  the 
method  of  making  Bordeaux  solution  on  a  large  scale.  What  is  meant 
by  a  4-4-50  Bordeaux  mixture  ? 

Ex.  305.  Try  an  experiment  in  your  locality  by  treating  some  oats 
seed  for  smut  according  to  paragraph  480  (formaldehyde).  Plant  this 
seed  on  a  plot  adjacent  to  one  on  which  untreated  seed  is  used  and  note 
results  at  harvest  time.  Send  to  your  Experiment  Station  for  bulletins 
on  treatment  of  oats  for  smut,  and  of  potatoes  for  scab. 


PART    III 

SOILS  AND  FERTILIZERS 

CHAPTER  L 
SOIL  FORMATION 

482.  Soil.     If  soil  is  examined  with  the  aid  of  a  micro- 
scope, it  is  found  to  consist  of  particles  of  rock  coated  with  a 
dark  substance,  which  has  been  derived  from  the  decomposi- 
tion of  organic  matter.     There  is  also  present  more  or  less 
vegetable  matter  consisting  of  fine  roots  and  other  parts  of 
plants.     The  rock  particles  vary  from  stones  of  consider- 
able size  to  grains  of  clay  that  are  less  than  one  five-thou- 
sandth of  an  inch  in  diameter.     Every  one  is  so  familiar 
with    the  existing  soil  that  it  is  hard  to  realize  that  nature 
required  ages  to  form  it  and  that  numerous  agencies  con- 
tributed to  the  process  of  soil  formation. 

483.  Weathering  of  Rocks.     All  soils  have  been  formed 
by  the  decay  or  weathering  of  solid  rock.     One  agency  in 
the  formation  of  the  soil  is  change  of  temperature.     A  rock 
like   granite,    for   instance,    consists   of   different   minerals 
cemented  together.     These  minerals  expand  and  contract 
at  different  rates  when  heated  or  cooled,  and  the  result 
is  that  changes  in  temperature  split  the  minerals  apart. 
Indeed,  even  a  mass  of  one  kind  of  material  is  disintegrated 
by  heat  if  the  changes  of  temperature  take  place  suddenly 
so  that  the  surface  and  the  interior  of  the  mass  are  unevenly 
heated.    The  surface  of  a  plate  or  of  a  piece  of  crockery, 

420 


SOIL  FORMATION 


421 


which  has  been  used  repeatedly  in  the  oven,  becomes  covered 
with  fine  cracks  caused  by  the  uneven  heating  and  cooling. 
The  same  thing  happens  in  the  case  of  some  of  the  soil- 
forming  recks.  More- 
over, rocks  are  more 
or  less  porous  and 
absorb  water  during 
the  rains.  In  cold 
weather  the  water 
freezes  and  expands 
with  great  force  and 
tends  to  break  the 
rocks  into  pieces  (6). 

484.  Running  water 
is  an  important  agency 
in    the    weathering    of 
rock.     The   water   al- 
ways carries  some  rock 
particles,     and      these 
rubbing  upon  the  bed 
of    the    stream    grind 
the    stone    to   powder, 
which  is  carried  away 

and  deposited  somewhere  to  form  a  soil.     The  more  rapid 
the  stream  the  greater  its  wearing  effect. 

485.  Glaciers  help  to  grind  the  rocks  to  powder.    The 
action   of   the   glaciers   in   Greenland,    Alaska,    and   other 
countries,  which  may  be  studied  at  the  present  time,  illus- 
trates what  happened  in  past  geologic  ages.     Many  thousand 
years  ago  a  large  area  of  the  northern  part  of  North  America 
was  covered  with  an  immense  glacier  that  pushed  its  way 
slowly  down  from  northern  Canada.     As  it  moved  south- 


FlG.   185.  —  The  disintegration  of  rocks  by 
heat,  cold,  and  frost. 


422 


SOILS  AND  FERTILIZERS 


ward  it  carried  with  it  large  quantities  of  rocks,  grinding 
them  against  one  another  until  they  were  reduced  to  parti- 
cles of  varying  degrees  of  fineness.  Such  great  force  had 

this  mass  of  ice  with 
the  rocks  imbedded  in 
it  that  it  planed  off 
the  tops  of  the  hills 
and  carried  the  debris 
with  it  to  the  south. 
Later,  when  the  climate 
became  warmer,  the 
ice  melted,  and  this 
rock  material  remained 

FIG.   186.  — The  formation  and  transportation         behind      to     become     a 

part    of   the    soil.     In 

some  sections  large  masses  of  this  material  were  left  as  long 
ridges  called  moraines. 

486.  Action  of  Winds.  In  some  parts  of  the  world 
winds  have  played  an  important  part  in  soil  formation. 
Wind  acts  chiefly  in 
transporting  materials ; 
but  in  localities  where 
it  blows  with  great 
violence  it  gathers  up 
and  sweeps  along  even 
coarse  sand  which, 
striking  against  rocks, 
slowly  wears  them 
away  and  is  itself 
made  finer.  In  the  western  part  of  this  country  may  be 
seen  instances  of  rock  carving  due  to  wind-driven  sand 
(Fig.  187). 


FIG.   187.  —  Peculiar  rock  forms  carved  by  the 
action  of  wind  and  sand. 


SOIL  FORMATION 


423 


487.  Chemical  Weathering.     Chemical  changes  in  rocks 
take  place  at  the  same  time  that  rocks  undergo  mechanical 
weathering,    or    pulverization.     While    the    original    rocks 
contain  all  the  mineral  elements  required  by  the  plant, 
these    elements   are   present    in   unavailable   forms.     Such 
rocks  as  the  granites  are  extremely  insoluble.     The  rains 
that  fall  on  these  rocks  contain  carbon  dioxide  in  solution, 
and  the  continued  action  of  this  weak  acid  results  in  a  par- 
tial decomposition  of  the  rock  and  a  change  of  some  of  the 
material  into  soluble  compounds.     In  this  way  some  of  the 
mineral  matter  finally  becomes  available  as  plant  food. 

488.  Plants  and  Soil  Formation.      Plants  play  an  im- 
portant part  in  soil  formation.     The  roots  act  both  me- 
chanically   and    chem- 
ically.     Nearly    every 

one  has  seen  examples 

of  the  enormous  force 

exerted  by  plant  roots 

in  breaking  apart  rocks 

(Fig.    188),  when    the 

plant  gets  started  in  a 

crevice  or  fissure.     The 

same  mechanical  action 

is  doubtless  exerted  by 

the  roots  on  the  rocks  underlying  some  soils.     The  roots  also 

secrete  an  acid  substance,  which  acts'  on  the  rocks  with 

which  they  come  in  contact ;    and  when  the  plants  die  and 

the  roots  decay  they  leave  in  the  soil  numerous  little  channels 

which  allow  the  passage  of  air  and  of  water  laden  with 

carbonic  acid. 

489.  Decaying   organic   matter    produces    humus,    and 
this  substance  in  its  turn  becomes  an  important  factor  in 


FlG.   188.  —  Growing  roots  of  tree  assisting  in 
soil  formation. 


424 


SOILS  AND   FERTILIZERS 


FIG.  189.  —  Decaying  organic  matter  assists 
in  soil  formation. 


soil  formation.  The  humus  increases  the  power  of  the  soil 
to  retain  water  and  to  supply  it  to  the  plant ;  and  since  all 
the  chemical  changes  by  which  plant  food  is  made  avail- 
able take  place  more  readily  in  the  presence  of  sufficient 

moisture,  it  will  be  seen 
that  this  moisture- 
holding  power  of  humus 
is  a  very  important  fac- 
tor in  soil  fertility. 
During  the  decay  of 
the  organic  matter,  car- 
bonic acid  and  other 
acid  substances  are  pro- 
duced, and  these  help  to 
dissolve  the  mineral  in- 
gredients of  the  soil  and 
change  them  into  substances  that  can  be  absorbed  by  plants. 

490.  Legumes   in    Soil   Building.     Plants    belonging   to 
the  clover  family,  the  so-called  leguminous  plants,  through 
the  bacteria  that  grow  in  the  nodules  or  tubercles  on  their 
roots,  are  able  to  use  the  free  nitrogen  of  the  air  as  a  source 
of  food  supply.     When  these  plants  die  and  become  incor- 
porated with  the  soil,  the  nitrogen  which  they  have  fixed 
becomes  a  part  of  the  soil  and  is  made  available  to  suc- 
ceeding plants.     It  has  been  estimated  that  from  50  to  150 
pounds  of  nitrogen  to  the  acre  may  be  fixed  in  this  way  in 
a  year.    This  power  of  the  leguminous  plants  to  accumulate 
nitrogen  is  probably  nature's  most  important  method  of  in- 
creasing the  nitrogen  content  of  the  soil  (168). 

491.  Animal  Life  in  the  Soil.     In  addition  to  the  processes 
described   above,  the  action  of  the  earthworms  and  other 
forms  of  animal  life  found  in  the  soil  should  be  mentioned. 


SOIL  FORMATION  425 

These  organisms  are  supposed  by  some  authorities  to  play 
a  very  important  part  in  the  working  over  of  the  soil  and 
in  its  preparation  for  plant  growth. 

EXERCISES 

Ex.  306.  Examine  a  sample  of  soil  under  a  magnifying  glass  or 
a  microscope.  What  material  can  you  distinguish  in  the  soil?  What 
can  you  say  about  the  sizes  of  the  rock  particles  ? 

Ex.  307.  What  is  meant  by  the  weathering  of  rock  ?•  Heat  and 
cool  a  piece  of  granite  repeatedly  and  note  whether  any  change  takes 
place.  Heat  a  piece  of  granite  in  a  flame  and  drop  it  into  cold  water. 
Does  the  sudden  change  of  temperature  affect  the  granite  ?  Notice  a 
plate  at  home  which  has  been  repeatedly  heated  in  the  oven.  What 
causes  the  cracks  on  the  surface?  Explain  how  heat  and  cold  help 
to  pulverize  the  rock. 

Ex.  308.  Recall  Ex.  5.  What  can  you  say  about  the  expansive 
force  of  freezing  water?  In  what  way  does  it  help  in  soil  formation? 

Ex.  309.  Explain  how  running  water  helps  in  pulverizing  the 
rocks.  Do  slow  or  rapid  streams  grind  the  rocks  more  readily?  How 
do  the  streams  form  their  valleys?  What  becomes  of  the  materials 
which  are  ground  to  powder  ? 

Ex.  310.  Explain  the  action  of  glaciers  in  forming  soils.  What 
part  of  North  America  was  covered  by  the  great  glacier?  What 
effect  did  the  glacier  have  on  the  topography  of  the  country?  What 
is  a  moraine?  Did  the  glacier  cover  your  locality?  If  so,  what  evi- 
dence of  that  fact  can  you  point  out?  Explain  the  action  of  winds  in 
rock  pulverization. 

Ex.  *311.  Explain  how  the  insoluble  silicates  are  made  more 
soluble  during  soil  formation.  What  is  the  original  source  of  the  nitro- 
gen in  soils  ?  What  can  you  say  of  the  first  plants  which  grew  on  the 
newly-formed  soils?  In  what  ways  is  organic  matter  important  in 
soil  formation  ?  How  do  the  roots  assist  in  disintegration  of  the  rocks  ? 
What  is  the  chief  function  of  the  legumes  in  building  soils  ? 

Ex.  312.  How  do  earthworms  affect  the  formation  of  soils?  Can 
you  find  lichens  growing  on  any  of  the  rocks  in  your  vicinity?  What 
is  the  appearance  of  the  rock  under  the  lichen  ?  How  do  you  explain 
this  appearance? 


CHAPTER  LI 

KINDS   OF   SOILS 

492.  Physical  Make-up  of  Soils.  From  the  last  chapter 
it  will  be  seen  that  the  completed  soil  consists  of  rock  parti- 
cles mixed  with  decaying  vegetable  matter,  the  decomposing 
remains  of  animals,  and  the  various  substances  formed  by 
chemical  action  from  the  rocks  and  organic  matter.  The 
rock  particles  are  classified  according  to  their  size  into 
gravel,  sand,  silt,  and  clay.  Gravel  is  subdivided  into 
coarse  and  fine  gravel,  and  at  least  four  grades  of  sand  are 
recognized :  coarse,  medium,  fine,  and  very  fine.  Silt  also 
is  divided  into  two  classes :  silt  and  fine  silt. 

The  individual  rock  particles  of  clay  are  the  smallest 
recognized  by  the  soil  physicist.  They  are  so  small  that 
they  cannot  be  distinguished  by  the  naked  eye,  nor,  indeed, 
can  they  be  felt  between  the  fingers.  In  other  words  the 
clay  is  entirely  without  grit,  and  when  it  is  rubbed  between 
the  fingers  only  the  smooth  mass  of  clay  can  be  felt,  the 
individual  particles  being  indistinguishable.  As,  clays 
are  very  adhesive  when  moist,  they  adhere  to  tillage  imple- 
ments. Moreover,  they  absorb  large  amounts  of  water; 
and  yet  the  individual  particles  lie  so  close  together  that 
water  poured  upon  the  surface  of  a  clay  often  remains  there 
a  long  time,  soaking  into  it  with  extreme  slowness.  Silt 
is  somewhat  coarser  than  clay  and  the  various  grades  of 
sand  are  still  coarser.  The  gravels  include  the  largest 
particles  that  are  recognized  as  belonging  to  a  true  soil. 

425 


KINDS  OF   SOILS 


427 


493 .  Classification  of  Soils.  Soils  are  classified  in  two  ways : 
(1)  as  to  the  method  of  their  formation,  and  (2)  as  to  their 
composition.     According  to  formation,  soils  are  divided  into 
sedentary  soils,  or  those  that  were  formed  where  they  now 
exist ;  and  transported  soils.     Sedentary  soils  are  subdivided 
into  residual  and  cumulose  soils.     Transported  soils  include 
alluvial,   colluvial,    drift,    and   ceolian   soils.      According   to 
composition,  soils  are  classified  into  clay,  sand,  loam,  and 
peat  soils. 

494.  Residual  soils,  which  have  been  made  from  the  decay 
of  the  rocks  on  which  they  lie  (Fig.  190),  partake  more  or 
less  of  the  composition  of  the  underlying  rocks.     They  have 
usually  lost  considerable  of  their  soluble  constituents  through 

RESIDUAL 
^ 


SSSSS'-S^ 

.hiehrr*^^  ?±^%* 


FIG.  190.  —  The  formation  of  residual,  colluvial,  and  alluvial  soils. 

the  solvent  action  of  rains.  These  soils  are  not  generally 
very  deep,  the  underlying  rock  being  comparatively  close  to 
the  surface.  Residual  soils  may  be  fertile  or  not,  their 
degree  of  fertility  depending  upon  the  kind  of  rock  from 
which  they  were  formed. 

495.  Cumulose  soils  are  those  formed  in  swamps  and 
marshes.  They  consist  largely  of  organic  matter  which 
has  come  from  the  partial  decay  of  the  marsh  plants.  They 


428 


SOILS  AND  FERTILIZERS 


FIG.  191.  —  The  formation  of  cumulose  soil. 


contain  also  the  earth  which  has  been  washed  down  from 
the  surrounding  higher  lands.     Muck  and  peat  are  examples 

of  cumulose  soils. 

496.  Alluvial  soils 
are  those  that  have 
been  carried  by  water 
and  deposited  some 
distance  from  their 
original  source.  They 
commonly  show  more 
or  less  distinct  layers 
as  a  result  of  the  fact 
that  the  coarser  parti- 
cles naturally  settle  first,  while  the  finest  particles  are  the 
last  to  be  deposited.  The  soils  in  river  valleys  are  alluvial 
and  have  been  carried  down  by  the  stream  during  the  flood 
season  and  deposited  as  the  velocity  of  the  current  de- 
creased. Alluvial  soils  are  usually  fertile,  but  it  will  be  seen 
that  the  character  of  these  soils  varies  with  the  character 
of  the  rock  material  of  the  uplands  from  which  they  are 
derived. 

497.  Colluvial  soils  are  formed  on  the  lower  slopes  of 
hillsides.     They  are  composed  of  particles  of  various  sizes 
that  have  moved  down  the  hillside  under  the  force  of  grav- 
ity.   (See  Fig.  190.) 

498.  Drift  soils  are  those  that  have  been  transported  by 
glaciers.     A  large  part  of  the  northern  United  States  is 
covered  by  drift  soils  that  were  carried  down  from  the  north 
by  the  great  glaciers  which  at  one  time  covered  this  region. 
Drift  soils  are  characterized  by  the  presence  of  bowlders 
and   rounded   pebbles.     They   vary   considerably   in   char- 
acter, and  many  different  kinds  of  soil  may  be  found  in  a 


KINDS  OF  SOILS  429 

single   farm   located   in   the   glaciated   region.     Drift   soils 
are  usually  very  productive. 

499.  ^Eolian  soils,  or  loess,  are  those  that  are  composed 
of  particles  transported  by  the  wind,  and  are,  therefore, 
sometimes  called  wind-formed  soils.     It  is  supposed  that 
considerable  areas  of  soils  in  the  central  United  States  are 
wind-formed.      They  vary  in  thickness  from  a  few  feet  to 
over  100  feet,  and  are  of  considerable  agricultural  value. 

500.  A  clay  soil  is  one  that  contains  over  sixty  per  cent 
of  clay  particles.     It  is  the  hardest  soil  to  work,  since  it  is 
sticky  when  wet  and  so  hard  that  it  can  hardly  be  pulverized 
when  dry.     In  very  dry  weather  clay  soils  crack  and  form 
openings  that  allow  excessive  evaporation  of  water,  a  condi- 
tion which  dries  and  injures  the  roots,  sometimes  breaking 
them.     Clay  soils,  unless  well  drained,  are  likely  to  be  cold 
and  unresponsive.     These  soils  are  usually  high  in  potential 
plant  food,  especially  potash,  but  require  careful  handling 
to  enable  the  plant  to  make  use  of  this  food  material.     They 
are  usually  retentive  of  added  plant  food  and  are,  there- 
fore, soils  that  can  be  liberally  fertilized  without  fear  of 
great  loss  of  the  applied  material. 

501.  Sandy  soils  are  those  containing  a  very  large  pro- 
portion of  sands  (75  per  cent  or  more).     They  are  just  the 
opposite  of  clay  soils,  being  too  open  and  porous,  while  the 
clays   are  too   compact   and   impervious.     They  hold   but 
little  water,  and  crops  growing  on  them*  are  likely  to  suffer 
in  hot,  dry  weather.     These  soils  are  usually  low  in  fertility 
and  have  little  power  to  retain  added  plant  food,  since  the 
soluble  material  in  manures  and  fertilizers  used  on  them  is 
likely  to  leach  through  them.     No  soil  is  so  poor  that  it 
cannot  be  made  to  grow  a  crop,  and  even  sandy  soils  can  be 
made  productive  by  the  liberal  use  of  organic  matter,  and  the 


430 


SOILS  AND   FERTILIZERS 


addition,  if  necessary,  of  lime,  phosphoric  acid,  and  potash. 
They  are  warm,  easily  worked  soils,  and  if  properly  handled 
are  often  profitably  used,  especially  for  early  truck  crops. 

502.  Peat  and   muck   soils  contain  very  large   amounts 
of  organic  matter,  some  of  them  having  as  much  as  80  per 
cent  of  such  matter.     They  are  found  in  the  beds  of  former 
lakes  or  swamps,  and  since  they  are  formed  by  the  partial 

decay  of  vegetable 
matter  under  water, 
they  usually  contain 
but  little  earth.  Peat 
is  an  intermediate  prod- 
uct between  vegetable 
matter  and  coal,  and 
perhaps  in  course  of 
time  it  would  be  con- 
verted into  coal.  The 
name  muck  is  some- 
times applied  to  a  soil 
in  which  the  organic 
matter  is  in  a  more  advanced  state  of  decay  than  it  is  in 
true  peat.  A  muck  contains  more  earth  than  the  peat  does 
and  is  more  compact.  These  soils  are  high  in  potential 
nitrogen,  but  are  usually  exceedingly  low  in  potash.  When 
they  are  well  drained  and  are  fertilized  with  phosphorus  and 
potash  they  are  generally  fertile  soils.  Many  of  the  black 
onion  soils  belong  to  this  type. 

503.  Loam  is  a  soil  consisting  of  a  mixture  of  clay,  silt, 
sand,  and  organic  matter   and   for  most   purposes  is  the 
most  desirable  type  of  soil.     Loam  soils  are  usually  well 
balanced,  since  they  hold  moisture  well,  are  well  supplied 
with  plant  food,  and  have  considerable  ability  to  retain 


FIG.  192.  —  Blocks  of  peat  being  dried  for  use 
as  fuel. 


KINDS  OJ1  SOILS  431 

such  soluble  plant  food  as  may  be  added  to  them.  They 
allow  the  air  to  circulate  through  them  more  freely  than 
clay  soils  do,  but  they  are  not  so  objectionably  open  as  are 
sandy  soils.  They  are  easily  worked  and  have  compara- 
tively little  tendency  to  bake  or  crust  on  the  surface.  They 
are  well  suited  to  most  crops  and  respond  well  to  fertiliza- 
tion. Several  subtypes  are  recognized :  (1)  heavy  clay 
loam,  (2)  clay  loam,  (3)  silt  loam,  (4)  sandy  loam,  (5)  light 
sandy  loam.  Taken  in  the  order  given  above  they  contain 
from  first  to  last  decreasing  quantities  of  clay,  and  increas- 
ing quantities  of  sand,  the  heavy  clay  loam  having  the 
most  clay  and  the  light  sandy  loam  the  most  sand.  These 
subtypes  naturally  partake  of  the  characteristics  of  their 
components,  so  that  the  heavy  clay  loam  shows  in  a  large 
measure  the  properties  of  a  clay,  and  the  light  sandy  loams 
are  only  a  step  removed  from  the  sandy  soils.  The  others 
are  intermediate  between  the  two  extremes.  The  loams  as 
a  whole  represent  the  more  common  types  of  farm  soils. 

504.  Light  and  heavy  soils  are  names  which  do  not,  as 
might  be  supposed,  refer  to  the  actual  weight  of  soils,  but 
to  the  ease  with  which  they  may  be  worked  with  tillage 
implements.  A  sandy  soil,  for  instance,  is  called  a  light 
soil,  although  it  actually  weighs  more  per  cubic  foot  than 
any  other  type  of  soil. 

EXERCISES 

Ex.  313.  What  are  the  four  general  classes  of  rock  particles  in 
soils?  How  are  these  classes  subdivided?  Which  particles  are  the 
smallest  ?  Work  up  a  little  pure  clay  with  water  and  rub  it  between 
the  fingers.  Do  you  feel  any  grit?  Do  the  same  with  a  sandy  soil, 
and  note  the  difference.  Place  about  two  tablespoonfuls  of  fine  soil  in 
a  quart  fruit  /jar  three  fourths  full  of  water.  Shake  the  jar  vigorously 
for  several  minutes,  let  it  stand  for  one  minute,  and  pour  the  muddy 


432 


SOILS  AND   FERTILIZERS 


water  into  a  second  jar.  The  sediment  remaining  in  the  first  jar  is 
composed  almost  entirely  of  sand.  Examine  it  carefully.  When  the 
second  jar  has  been  standing  five  minutes  pour  off  the  muddy  water  into 
a  third  jar ;  add  more  water,  shake  this  jar  vigorously,  and  after  it  has 
stood  five  minutes  pour  off  the  water.  The  sediment  remaining 
in  the  second  jar  is  largely  silt.  Let  the  third  jar  stand  at  least  two 
hours  and  then  pour  off  the  water.  The  residue  in  this  case  is  largely 
clay.  Note  how  fine  the  particles  are.  Examine  them  under  a  micro- 
scope. Can  you  find  samples  of  clay,  silt,  and  gravel  in  your  vicinity? 
Ex.  314.  What  are  the  two  general  classes  of  soils  according  to 
formation?  Are  the  soils  in  your  vicinity  sedentary  or  transported 
or  both?  What  are  residual  soils?  Cumulose  soils?  Can  you  find 
either  type  near  the  school  ?  What  is  meant  by  allu- 
vial, colluvial,  drift,  and  aeolian  soils?  How  many 
of  these  can  you  find  near  your  home?  How  can 
you  tell  a  drift  soil  ?  Walk  along  a  stream  and  note 
how  the  rock  particles  of  varying  sizes  are  deposited 
by  the  stream  as  the  current  becomes  less  rapid. 

Ex.  315.  What  are  the  chief  characteristics  of 
a  clay  soil?  Of  a  sandy  soil?  Of  a  muck  soil? 
Why  are  clay  soils  more  difficult  to  cultivate  than 
sandy  soils  ?  Which  hold  more  water  ?  Which 
contain  more  plant  food?  Are  there  any  areas  of 
muck  soils  in  your  locality  ?  For  what  are  they  used  ? 
Ex.  316.  What  is  meant  by  a  loam  ?  Why  are 
loam  soils  desirable  ?  What  general  classes  of  loam 
soils  are  recognized  ?  How  many  of  them  can  you 
find  in  your  locality?  Bring  samples  of  as  many 
different  kinds  of  soil  as  you  can  find  to  the  school 
and  classify  them  according  to  this  chapter.  (The 
best  method  of  obtaining  a  sample  of  soil  is  by 
means  of  the  soil  auger  (Fig.  193),  which  is  made  by 
welding  a  three-eighths  inch  gas  pipe  to  a  one  and 
one-fourth  inch  wood  auger.  The  class  should  take 
an  excursion  over  the  neighboring  farms  and  by  the  means  of  the  soil 
auger  locate  as  many  soil  types  as  possible.) 


FIG.  193.  —  A  soil 
auger. 


CHAPTER  LIT 

RELATION   OF  THE   SOIL  TO   PLANTS 

505.  Permeability  to  Plant  Roots.    The   soil   furnishes 
an  anchorage  for  the  plant  roots  and  enables  them  to  hold 
the  plant  in  an  upright  position.     Since  the  roots  of  the 
ordinary  farm  crops  must  penetrate  into  the  soil  to  a  dis- 
tance of  from  two  to  ten  feet  in  order  to  obtain  the  necessary 
amount  of  plant  food,  the  permeability  of  the  soil  is  a  matter 
of  great  importance.     A  soil  that  is  so  compact  as  to  hinder 
the  growth  of  the  roots,  or  one  that  has  near  the  surface  a 
hardpan   through  which  the  roots    cannot  penetrate,  seri- 
ously interferes  with  the  full  development  of   the  plant. 
Since  the  cells  of  the  growing  points  of  the  roots  need  oxygen 
for  respiration,  it  follows  that  the  soil  must  be  permeable 
to  air  as  well  as  to  the  plant  roots. 

506.  Water-holding    Capacity.     Attention    has    already 
been  called  to  the  enormous  amount  of  water  required  for 
plant  growth   (346).     The  plant  needs  water  during  the 
entire  growing  season,  and  as  the  rains  are  irregular  and 
often  come  weeks  apart,  the  soil  must  act  as  a  reservoir  for 
moisture.     The  water-holding  capacity 'of  the  soil,  then,  is 
a   factor   of   great   importance.     The   proper   condition   of 
moisture  in  the  soil  is  the  most  important  single  factor  in 
determining  the  fertility  of  the  land,  and  the  failure  of  soils 
to  produce  good  crops  is  more  often  due  to  lack  of  available 
water  than  to  any  other  one  cause.    Any  plan  that  will 
increase  the  capacity  of  the  soil  to  store  water  is  desirable <> 

EV.  CHEM.— 28  433 


434  SOILS    AND    FERTILIZERS 

507.  The  Soil  Supplies  Nitrogen.    All  plants  except  the 
legumes  are  dependent  upon  the  nitrates  in  the  soil  for 
their  supply  of  nitrogen.    Although  a  good  soil  may  con- 
tain from  three  to  five  thousand  pounds  of  nitrogen  to  the 
acre  in  the  surface  foot,  only  a  few  pounds  of  it  is  in  the  form 
of  nitrates.     Nearly  all  the  nitrogen  is  present  in  organic 
matter ;     but    in    these    complex    organic    compounds    it 
cannot  be  utilized  by  plants.     Nitrification  (168),  therefore, 
is  necessary  to  the  maintenance  of  the  fertility  of  the  soil. 
Nitrification  takes  place  only  when  the  temperature  of  the 
soil  is  more  than  five  degrees  above  freezing,  and  becomes 
more  rapid   with   rise   of  temperature.    Hence,   it   ceases 
during  the  winter  months  and  is  most  vigorous  during  the 
hot  months  of  midsummer.    The  nitrifying  bacteria  cannot 
live  without  a  sufficient  supply  of   oxygen,  and   for  this 
reason  stirring  the  soil  to  introduce  air  increases  the  rate 
of  nitrification.      Moreover,   these  bacteria  cannot  thrive 
in  a  soil  that  is  acid,  hence  carbonate  of  lime  is  essential 
to  nitrification.    So  vital  is  the  process  of  nitrification  to 
the  growing  crop  that  successful  agriculture  depends  largely 
upon  providing  proper  conditions  for  rapid  nitrification. 

508.  Denitrification.    While  the  nitrifying  bacteria  may 
be  said  to  be  the  farmer's  friends,  there  are,  unfortunately, 
other  organisms  in  the  soil  that  produce  evil  results.     One 
class  of  these,  known  as  denitrifying  bacteria,  decomposes  the 
nitrates,  and,  perhaps,  some  other  nitrogenous  compounds, 
with  the  final  result  that  the  nitrogen  is  set  free  and  returned 
to  the  air  in  its  elemental  condition.    This  process,  of  course, 
robs  the  soil  of  a  part  of  its  nitrogen,  and  is  especially  un- 
fortunate because  it  removes  the  part  that  was  most  readily 
available  to  the  crop.     Denitrification  can  be  prevented  by 
providing  the  conditions  that  favor  rapid  nitrification. 


RELATION  OF  THE   SOIL  TO  PLANTS 


435 


509.  Fixation  of  Nitrogen.     Leguminous  plants  are  not 
absolutely  dependent  upon  the  nitrates  of  the  soil.     These 
plants  use  the  nitrates  as  long  as  they  are  available;    but 
when  the  soil  fails  to  supply  nitrates  in  sufficient  quantity, 
they  depend  upon  the  nodule-forming  bacteria,  and   thus 
indirectly  make  use  of  free  nitrogen.     The  fixation  of  nitro- 
gen is  not  a  function  of  the  legume  itself,  but  of  the  bac- 
teria that  produce  the 

nodules;  and  in  the 
absence  of  these  organ- 
isms the  legumes  are 
quite  as  dependent  up- 
on the  supply  of  ni- 
trates as  are  the  other 
families  of  plants.  In 
soils  very  rich  in  ni- 
trogen the  root  tuber- 
cles may  not  be  formed 
on  legumes  even  when 
the  proper  bacteria  are 
present.  In  ordinary 
soils  a  crop  of  clover 
obtains  one  third  of  the 
nitrogen  from  the  soil 
and  two  thirds  from  the 
air. 

510.  Inoculation     of 
Soils.    Experience    has 
shown  that  not  all  soils 
contain     the     bacteria 

necessary  to  the  fixation  of  free  nitrogen  by  legumes. .  These 
bacteria  may  be  introduced  into  a  field  by  scattering  on  it 


FIG.  194.  —  Effect  of  inoculation  of  soil  on 
growth  of  soy  bean.  The  plant  on  the  left  was 
grown  in  inoculated  soil ;  that  on  the  right, 
without  inoculation. 


436  SOILS  AND  FERTILIZERS 

a  small  quantity  of  soil  from  a  field  in  which  the  same 
legume  has  been  successfully  grown,  and  then  harrowing 
it  in.  Nitrogen-fixing  bacteria  that  grow  on  one  kind  of 
legume  will  not  thrive  on  all  other  legumes.  Therefore  the 
soil  from  a  red  clover  field  is  not  suitable  for  inoculating  soil 
for  soy  beans  or  alfalfa.  Soils  on  which  sweet  clover  grows, 
however,  may  be  used  to  inoculate  for  alfalfa. 

Inoculation  of  the  soil  is  of  undoubted  use  in  some  cases ; 
but  there  is  danger  of  overestimating  its  value.  It  must 
not  be  regarded  as  a  panacea  for  all  the  ills  of  the  soil.  Inocu- 
lating a  soil  simply  introduces  the  nodule-forming  bacteria, 
and  if  the  failure  of  a  leguminous  crop  was  due  only  to 
absence  of  these  bacteria,  inoculation  will  be  beneficial.  It 
will  in  no  wise  overcome  failure  resulting  from  bad  seed, 
improper  preparation  of  the  ground,  adverse  weather  condi- 
tions, or  acidity  of  the  soil;  and  the  farmer  should  assure 
himself  that  the  soil  conditions  are  as  favorable  as  possible 
before  he  attempts  inoculation. 

511.  Mineral  Elements.  It  has  been  shown  that  seven 
elements  are  necessary  to  plant  growth  (350).  Of  these, 
only  phosphorus,  potassium,  and  calcium  need  be  consid- 
ered, since  experience  seems  to  show  that  the  others  are 
present  in  all  soils  in  sufficient  quantities  for  maximum 
crop  production.  The  amounts  of  nitrogen,  phosphorus, 
and  potassium  removed  by  crops  seem  insignificant  when 
compared  with  the  total  quantities  of  these  elements  that 
are  present  in  a  good  soil.  The  grain  and  straw  of  a  thirty- 
bushel  crop  of  wheat,  for  example,  remove  from  an  acre 
60  pounds  of  nitrogen,  10  pounds  of  phosphorus,  and  35 
pounds  of  potassium.  The  first  foot  of  a  good  loam  soil, 
however,  contains  to  each  acre  about  5000  pounds  of  nitro- 
gen, 2200  pounds  of  phosphorus,  and  35,000  pounds  of  po- 


RELATION   OF  THE   SOIL  TO  PLANTS  437 

tassium.  Such  a  soil,  therefore,  has  sufficient  nitrogen  for 
80  crops  of  wheat  of  30  bushels  each,  phosphorus  enough 
for  220  such  crops,  and  potassium  enough  for  1000  crops. 
Yet  it  is  well  known  that  such  a  soil  would  not  produce  even 
eighty  such  crops  of  wheat  in  succession. 

512.  Chemical  Analyses.     A  chemical  analysis  gives  the 
total    amounts    of   nitrogen,  phosphoric   acid,  and   potash 
in   the  soil,   but   does    not    indicate   what  part   of   these 
substances  is  available  to  the  plant.     The  greater  propor- 
tion of  these  substances  is  locked  up  in  insoluble  compounds, 
in  which  form  the  plant  is  incapable  of  using  them.     Smaller 
quantities  have  been  changed  by  the  forces  of  nature  into 
a  condition  in  which  they  are  available  to  plants.    While 
the  amounts  of  these  materials  removed  by  the  crop  seem 
insignificant  when  compared  with  the  total  plant  food  in 
the  soil,  they  may  be  very  large  in  comparison  with  the  avail- 
able* part.    The  unavailable,   or  potential,   plant  food   is 
gradually   being  made   available,   but  not  with   sufficient 
rapidity  to  replace  that  removed  from  the  field  at  harvest. 
It  will  thus  be  seen  that  the  present  fertility  of  the  soil  de- 
pends not  upon  the  potential  plant  food  it  contains  but 
upon  that  which  is  immediately  available  to  the  plant.     A 
chemical  analysis  is  of  value,  however,  in  showing  the  po- 
tential possibilities  of  a  soil. 

513.  Limiting  Factors.     Since  a  definite  amount  of  each 
element  of  plant  food  is  required  for  a  certain  yield,  and 
since  none  of  the  elements  can  be  replaced  by  another  (350), 
it  follows  that  the  crop  produced  will  be  limited  by  the  quan- 
tity of  the  essential  element  present  in  least  proportion, 
compared  with  the  requirements   of  the   crop.     In   other 
words,  if  a  field  of  corn  can  obtain  phosphorus  sufficient  for 
only  half  a  crop,  no  more  than  this  can  be  produced  no  matter 


438  SOILS  AND  FERTILIZERS 

how  much  of  the  other  elements  of  plant  food  is  present. 
The  substance  which  thus  limits  the  crop  production  is 
said  to  be  the  limiting  factor  for  that  soil.  The  maximum 
yield  of  a  particular  field  is  often  determined  by  some  one 
factor,  and  it  is  important  to  discover  what  that  limiting 
factor  is  and  to  apply  a  remedy.  The  lack  of  sufficient  water 
is  the  most  common  limiting  factor;  phosphorus  probably 
ranks  second ;  and  either  calcium  carbonate  or  nitrogen 
ranks  third.  Potassium  is  the  usual  limiting  factor  in  peat 
and  muck  soils. 

514.  Nature's  Methods  Contrasted  with  Those  of  Man. 
The  amount  of  vegetation  which  the  soil  can  produce  has 
been  constantly  increasing.  Under  natural  conditions  this 
growth  is  not  removed  from  the  ground,  and  the  plant  food 
therein  is  again  made  available,  so  that  the  land  is  con- 
stantly increasing  in  fertility.  Thus  the  fertility  of  virgin 
soils  is  the  result  of  accumulations  due  to  a  variety  of  forces 
acting  through  countless  ages,  during  which  little  has  been 
removed  from  the  soil  while  much  has  been  added  thereto. 

Man,  on  the  contrary,  has  reversed  this  process,  and  while 
adding  little  to  the  soil  has  removed  much  therefrom. 
Through  the  constant  harvesting  of  crops,  and  the  leaving 
of  the  ground  bare  and  exposed  to  the  action  of  the  elements, 
he  is  rapidly  depleting  nature's  store  of  food,  and  the  yield 
steadily  becomes  smaller.  To  prevent  exhaustion  of  the 
soil  it  becomes  necessary,  therefore,  for  him  to  assist  nature 
in  making  potential  plant  food  available  and  to  return  to 
the  soil  at  least  a  part  of  that  which  he  removes  in  the  crops. 

EXERCISES 

Ex.  317.  Why  must  the  soil  be  permeable  to  plant  roots  ?  What 
does  the  plant  obtain  from  the  soil?  Must  the  oxygen  of  the  air 
penetrate  into  the  soil  ?  Examine  a  section  of  soil  in  an  excavation. 


RELATION  OF  THE   SOIL  TO  PLANTS  439 

Ex.  318.  Place  100  grams  of  a  thoroughly  dried  soil  in  a  beaker, 
add  100  cubic  centimeters  of  water,  and  stir  for  several  minutes.  Place 
a  folded  filter  paper  in  a  funnel  and  moisten  the  filter.  When  water 
no  longer  drips  from  the  filter,  place  a  100  cc.  graduated  cylinder  under 
the  funnel  and  pour  the  mixture  of  soil  and  water  into  the  filter.  When 
water  ceases  to  drip  from  the  funnel  measure  the  water  which  has  run 
through.  The  number  of  cubic  centimeters  of  water  in  the  cylinder 
subtracted  from  100  represents  in  percentage  the  water-holding  capacity 
of  the  soil.  Repeat  the  exercise  with  a  sandy,  clay,  and  loam  soil. 
Compare  results.  Why  is  the  water-holding  capacity  of  the  soil  im- 
portant ? 

Ex.  319.  In  what  form  do  most  plants  use  nitrogen?  Is  the  pro- 
cess of  nitrification  very  important?  At  what  time  of  the  year  is 
nitrification  most  active?  What  are  the  soil  conditions  necessary 
for  nitrification?  Why  is  denitrification  undesirable?  Under  what 
soil  conditions  does  denitrification  proceed  most  rapidly  ? 

Ex.  320.  Dig  up  a  clover  plant  or  other  legume  and  wash  the 
dirt  from  the  roots.  (Do  not  shake  dirt  loose.)  What  connection 
have  the  nodules  on  the  roots  with  the  nitrogen  supply  ?  Will  legumes 
form  nodules  in  soils  rich  in  nitrogen?  Is  the  fixation  of  nitrogen  a 
function  of  the  legume  or  of  the  nodule  bacteria  ? 

Ex.  321.  What  proportion  of  its  nitrogen  does  clover  obtain  from 
the  air  and  what  proportion  from  the  soil?  Make  a  collection 
for  the  school  of  the  different  root  nodules  in  your  neighborhood  and 
preserve  them  in  water  with  a  10  per  cent  solution  of  commercial  form- 
aldehyde. 

Ex.  322.  Do  all  soils  contain  the  proper  bacteria  for  the  fixation 
of  nitrogen  by  legumes?  Do  the  same  kind  of  bacteria  work 
with  all  legumes?  How  may  the  bacteria  be  introduced  into  a  soil 
in  which  they  are  lacking?  To  what  extent  *is  inoculation  of  soils 
valuable  ?  Will  inoculation  take  the  place  of  other  preparation  of  the 
ground  ? 

Ex.  323.  Which  of  the  elements  of  plant  food  are  likely  to  be 
deficient  in  the  soil?  What  does  a  chemical  analysis  tell  about  the 
fertility  of  the  soil  ?  Explain  what  is  meant  by  available  and  potential 
plant  food  ?  What  is  meant  by  a  limiting  factor  in  plant  growth  ? 
What  are  the  more  common  limiting  factors  in  plant  growth?  Con- 
trast nature's  methods  in  regard  to  the  soil  with  those  of  man. 


CHAPTER  LIII 

SOIL  WATER 

515.  Structure  of  Soil.    A  careful  examination  of  the  soil 
shows  that  it  is  made  up  of  grains  of  various  sizes  fitted 
somewhat  loosely  together,  with  spaces  between  them  which 
are  as  variable  in  size  as  the  grains  themselves.     In  a  loam 
soil  in  good  tilth  the  spaces  between  the  grains  represent 
about  half  the  total  volume  of  the  soil. 

516.  Ground  Water.     In  the  surface  soil  the  spaces  be- 
tween the  grains  are  usually  filled  with  air,  but  at  some  dis- 
tance below  the  surface  the  spaces  are  entirely  filled  with 
water.     This  water  is  known  as  ground  water.     The  upper 
surface  of  the  ground  water  is  called  the  water  table.     The 
exact  height  of  the  water  table  may  be  ascertained  by  sink- 
ing a  hole  to  such  a  depth  that  water  will  stand  in  it,  the 
level  of  the  water  in  the  hole  being  practically  that  of  the 
water  table.     It  is  ground  water  that  supplies  wells  and 
springs. 

517.  Free  Water  and  Film  Water.     After  a  rainy  period 
the  ground  may  become  saturated  with  water.     In  such  a 
case  the  water  table  is  at  the  surface.    The  water  table 
gradually  sinks,  and  after  a  few  days  of  dry  weather  it  may 
be  a  foot  or  more  below  the  surface.     The  soil  water  that  has 
drained  downward  by  the  pull  of  gravity  is  called  free,  or 
gravitational,   water.     The   water  that  remains   above   the 
water  table  is  called  film  water.     The  following  experiment 
will  make  clear  the  difference  between  free  water  and  film 

440 


SOIL  WATER 


441 


WATER 
TABLE 


GROUND 
WATER 


water.  Cork  tightly  the  opening  at  the  bottom  of  a  flower 
pot.  Add  soil  to  the  pot  until  it  is  nearly  full.  Then  pour 
in  water  until  the  soil  is  saturated.  When  this  condition  is 
reached  the  water  table  is  at  the  surface  of  the  soil.  Now 
remove  the  cork,  and  much  of  the  soil  water  will  drain  off. 
This  is  free  water.  The 
water  that  remains  in 
the  soil  exists  as  thin 
films  of  moisture  around 
the  grains  of  soil.  These 
films  join  where  the  soil 
grains  touch  one  another 
and  really  make  one  con- 
tinuous film  of  moisture 
throughout  the  soil.  This 
film  moisture  is  also 
called  capillary  water  be- 
cause it  moves  through 
the  soil  by  capillary  at- 
traction as  oil  moves  up- 
ward through  a  lamp  wick. 

518.  Movement  of  Film  Water.  The  tendency  in  the 
soil  is  to  maintain  an  even  thickness  of  film  water  over  all 
the  soil  grains ;  consequently  if  anything  happens  to  decrease 
the  thickness  of  the  film  in  one  part  of  the  soil,  water  will 
move  toward  that  point  to  restore  equilibrium.  When 
water  evaporates  from  the  surface  of  the  soil,  more  water 
moves  upward  to  replace  the  loss.  This  movement  is  known 
as  the  capillary  rise  of  water.  It  will  thus  be  seen  that 
evaporation  not  merely  dries  the  surface  of  the  soil  but 
actually  pumps  up  water  from  the  lower  layers  and  affects 
the  water  content  of  the  soil  for  some  distance  below  the 


FIG.  195.  —  Sectional  view  of  soil  showing 
ground  water  and  film  moisture. 


442 


SOILS  AND   FERTILIZERS 


surface.  The  rate  and  the  amount  of  capillary  movement 
depend  upon  the  structure  of  the  soil.  The  coarser  the  soil 
the  more  rapid  the  rise  of  water  by  capillarity,  but  the  finer 
the  soil  the  higher  the  water  will  be  lifted.  A  very  coarse 
sand  may  raise  the  water  only  a  few  inches,  a  fine  sandy 


FIG.  196.  —  Relation  of  the  water  table  to  contour  of  the  land. 

loam  will  lift  it  a  few  feet,  while  in  a  clay  soil  the  water  will 
rise  at  least  twenty-five  feet.  If  the  soil  is  made  more  com- 
pact, the  capillary  rise  of  water  is  increased. 

519.  How  Plants  Get  Their  Water.    The  roots  of  the 
plant  push  their  way  down  between  the  soil  grains,  branch- 
ing more  or  less  and  spreading  throughout  the  soil.     The 
root  hairs  at  the  growing  points  of  the  roots,  which  are  the 
absorbing  organs  of  the  plant,  work  their  way  in  between 
and  around  the  small  soil  grains,  adhering  very  closely  to 
them.     The  root  hairs  absorb  the  water  of  the  film  moisture, 
and  as  they  reduce  the  thickness  of  the  film,  more  water 
diffuses  to  the  point  of  absorption.     Since  the  root  hair  gets 
all  its  water  and  food  from  the  film  on  the  surface  of  the 
soil  grains,  film  moisture  is  a  desirable  form  in  which  to  have 
water  in  the  soil. 

520.  High  Water  Table  Objectionable.   The  crops  are  sure 
to  suffer  when  the  level  of  the  ground  water  is  near  the  sur- 
face of  the  soil  (Fig.  197).    A  high  water  table  limits  the  feed- 
ing space  available  to  the  plant  and,  consequently,  the  amount 


SOIL  WATER  443 

of  food  it  can  obtain.  The  plants  that  are  of  agricultural 
importance  must  have  their  roots  supplied  with  air,  and 
such  plants  do  not  send  their  roots  below  the  water  table 
because  the  spaces  between  the  soil  grains  below  this  level 
are  filled  with  water,  a  condition  which  prevents  the  entrance 
of  air.  The  depth  to  which  the  roots  will  go,  then,  depends 
upon  the  position  of  the  water  table.  • 

Free  water  near  the  surface  is  also  objectionable  because 
it  makes  the  soil  cold.  It  requires  much  more  heat  to  warm 
water  a  certain  number  of  degrees  than  to  raise  the  tempera- 
ture of  an  equal  weight  of  the  dry  matter  of  the  soil  the 
same  number  of  degrees.  Hence  a  soil  that  contains  much 
water  is  harder  to  heat  than  one  that  is  comparatively  dry. 

A  very  wet  soil  causes  plant  food  to  become  locked  up  in 
unavailable  forms,  and  in  some  cases  brings  about  the  pro- 
duction of  compounds  that  are  actually  poisonous  to  the 
desirable  plants.  An  excessive  amount  of  water  in  the 
soil  also  dilutes  the  plant  food  in  solution  and  makes  it 
more  difficult  for  the  plant  to  procure  sufficient  nourishment. 

One  of  the  most  important  considerations  in  this  connec- 
tion is  the  fact  that  the  presence  of  free  water  in  the  soil 
prevents  nitrification  and  promotes  denitrification.  In 
water-logged  soil,  nitrates  are  rapidly  decomposed,  the  nitro- 
gen being  given  off  to  the  air  in  the  free,  or  elemental,  con- 
dition; and  for  this  reason  not  only  is  nitrogenous  food 
in  the  soil  destroyed,  but  the  application  of  nitrogen  ferti- 
lizers to  such  a  soil  results  in  great  waste  of  this  valuable 
element. 

521.  Underdrainage.  When  the  water  table,  during 
much  of  or  all  the  growing  season,  is  nearer  than  three  feet 
to  the  surface  of  the  ground,  some  system  of  underdrainage 
becomes  necessary,  if  the  best  results  in  crop  production 


444 


SOILS  AND  FERTILIZERS 


are  to  be  achieved.  This  is  best  accomplished  by  means 
of  drain  tile.  The  benefits  of  tile  drainage  are  summarized 
in  the  following  paragraphs. 

The  water  table  is  lowered  to  the  level  of  the  drain  tile, 
the  water  running  off  through  the  tile  instead  of  remaining 
in  the  soil  as  stagnant  water.  The  plant  roots  can  now  pene- 
trate the  soil  to  a  greater  depth,  since  air  follows  the  water 


FIG.  197.  —  Effect  of  lack  of  drainage  on  root  growth.  The  high  water  table 
shown  on  the  left  limits  the  feeding  space  of  the  roots,  and  in  time'of  drought, 
as  shown  on  the  right,  the  plant  suffers  because  of  its  shallow  roots  and  lack 
of  moisture. 

as  it  percolates  downward,  thus  ventilating  the  soil.  This 
ventilation  is  of  great  importance  and  it  is  continuous,  since 
each  rain  forces  some  of  the  old  air  out  of  the  soil,  and  the 
new  air  following  the  rain  takes  its  place. 

In  a  well-drained  area,  more  of  the  rain  will  soak  into  the 
soil  instead  of  running  off  the  surface ;  thus  surface  washing 
of  the  soil  will  be  prevented  to  some  extent.  Ideal  conditions 
demand  that  there  shall  be  no  run-off  at  all,  and  the  farmer 
should  strive  to  attain  as  nearly  to  this  ideal  as  is  practicable. 


SOIL   WATER 


445 


In  some  countries,  where  terrace  farming  is  followed,  the  run- 
off is  almost  entirely  eliminated. 

The  spring  rains  are  usually  warm,  and  it  is  desirable 
to  have  them  percolate  through  the  soil.  Tile-drained 
soils  warm  up  earlier  in  the  spring,  stay  warm  later  in  the 
fall,  and  maintain  a  higher  temperature  throughout  the  grow- 
ing season  than  do  undrained  soils.  This  is  partly  due  to 


FiQ.  198.  —  Effect  of  proper  drainage  on  root  growth. 

the  fact  that  more  evaporation  takes  place  from  the  surface 
of  the  undrained  soil  (8).  For  these  reasons  crops  on  well- 
drained  soils  have  a  longer  season  for  growth. 

Tile  drainage  promotes  nitrification  and  prevents  denitri- 
fication.  The  decay  of  organic  matter,  resulting  in  the 
production  of  nitric  acid,  is  an  oxidizing  process  and  can 
take  place  only  in  a  well- ventilated  soil. 

Many  thousands  of  square  miles  of  waste  land  have  been 
reclaimed  by  means  of  tile  drainage.  In  the  case  of  swamps, 
marshes,  and  ponds  the  water  table  is  actually  at  or  above 


446  SOILS  AND  FERTILIZERS 

the  surface  of  the  ground,  and  such  lands  will  not  produce 
the  ordinary  farm  crops  at  all  until  they  are  drained. 

522.  Drainage    Reduces    Injury   from   Drought.     Para- 
doxical as  it  may  seem,  underdraining  increases  the  amount 
of  water  available  to  the  plant.     The  crop  depends  almost 
entirely  on  the  capillary  or  film  moisture  for  its  supply  of 
water,  and  the  roots  do  not  enter  that  part  of  the  soil  con- 
taining free  water.     Lowering  the  water  table  greatly  in- 
creases the  total  amount  of  film  moisture,  as  all  that  part  of 
the  soil  from  which  the  free  water  has  been  removed  is 
capable  of  holding  capillary  water.    Thus  it  will  be  seen  that 
while  the  total  amount  of  water  in  the  soil  is  decreased  by 
drainage,  that  amount  which  is  of  use  to  the  plant  is  made 
much  greater.     Drainage  prevents  injury  from  drought  also, 
by  allowing  plants  to  make  deeper  root  growth,  hence  they 
are  not  so  easily  affected  by  the  extreme  drying  of  the  sur- 
face of  the  ground  that  takes  place  in  times  of  scanty  rainfall. 

523.  No    Useful    Water    Lost    Through    Tiles.     It    will 
readily  be  seen  that  tile  draining  determines  the  highest 
point  the  water  table  can  reach,  but  in  dry  weather  the  level 
of  the  ground  water  may  be  much  below  the  drain.     It  is 
sometimes  feared  that  for  this  reason  a  part  of  the  water 
from  summer  rains  may  be  lost  through  the  tile.     Experi- 
ence has  shown,  however,  that  the  water  does  not  percolate 
into  the  drain,  as  some  suppose,  but  that  the  drains  remove 
water  only  when  there  is  sufficient  rain  to  raise  the  water 
table  to  the  level  of  the  tile.    It  is  simply  the  excess  of  water 
that  is  removed  by  the   underdraining,  and  not  the  part 
that  is  of  importance  to  the  plant. 

524.  Drainage    Sometimes   Beneficial   on   High   Lands. 
Strangely  enough,  experience  has  shown  that  it  is  not  merely 
low-lying   soils   that   are   benefited  by  underdraining.     In 


SOIL  WATER 


447 


many  cases  heavy  clay  soils  in  elevated  positions,  especially 
if  underlaid  by  rather  impervious  subsoils,  are  greatly  im- 
proved by  tiling.  In  such  soils  the  percolation  is  so  slow 
that  practically  the  same  effect  is  produced  as  would  be 
expected  if  the  general  level  of  the  ground  water  were  near 
the  surface.  These  soils  are  made  more  mellow  by  drainage 
and  respond  more  readily  to  early  tillage.  In  fact,  it  may 
be  said  that  it  will  pay  to  tile  drain  any  soil  that  has  a  clay 
subsoil,  no  matter  what  the  elevation  or  slope  of  the  land. 

525.   Draining  the  Farm.     The  laying  out  of  a  complete 
system  of  drainage  calls  for  the  services  of  a  skilled  drainage 


FIG.  199. —  A,  Drainage  system  for  level  land.     B,  Drainage  system  where 
there  is  much  variation  in  the  slope  of  the  land. 

engineer,  especially  if  the  farm  is  very  level.  The  more 
fall  there  is  to  the  land,  the  easier  it  is  for  an  unskilled  person 
to  lay  drains  that  will  work.  Since  the  tile  must  be  se  laid 


448 


SOILS  AND  FERTILIZERS 


as  to  give  a  uniform  fall  from  the  highest  point  to  the  out- 
let, the  planning  of  the  system  should  be  preceded  by  a 
survey  of  the  farm  for  that  purpose.  When  the  field  to 
be  drained  is  broad  and  level  (Fig.  199^1),  the  main  drains 
and  laterals  are  uniformly  spaced ;  but  often  the  ground  has 
natural  drainage  lines  (Fig.  199  B)  along  which  it  is  usually 
best  to  run  the  ditches,  especially  the  main  lines. 

The  size  of  the  tile  should  vary  with  the  area  to  be 
drained  and  with  the  grade  at  which  the  tile  is  laid.  With 
an  average  fall  of  one  inch  to  one  hundred  feet,  a  four- 
inch  tile  will  drain  ten  acres.  With  a  greater  fall  this  size 
of  tile  would  remove  the  water  from  a  larger  area. 

The  depth  at  which  the 
tile  is  placed  and  the 
distance  between  the  lines 
of  tile  depend  upon  the 
character  of  the  soil.  The 
more  compact  the  soil  the 
nearer  together  the  lines 
of  tile  and  the  less  the 
depth.  In  very  heavy 
clays  the  drains  should 
not  be  farther  than  two 
rods  apart,  while  in  lighter 
soils  the  distance  apart 
may  be  twice  as  great. 
Clay  soils  should  have  the 
drains  placed  about  thirty 
inches  deep ;  but  in  light  soils  the  tile  may  be  as  much  as 
four  feet  below  the  surface. 

Unglazed  clay  tile  are  the  more  common.  Glazed  tile 
may  be  used,  however,  since  all  the  water  enters  at  the  joints 


FIG.  200.  —  Drainage  machine  at  work. 


SOIL  WATER 


449 


and  there  is  no  advantage  in  having  porous  tile.     Machines 
are  now  on  the  market  for  making  tile  from  cement. 

The  ditches  for  laying  the  tile  are  often  dug  by  hand, 
and  various  special  tools  have  been  devised  for  use  in  ditching 
as  well  as  for  laying  the 
tile.  Machines  worked 
by  horse  power  and  by 
tractors  (Fig.  200)  are 
used  in  ditching,  when 
the  character  of  the  soil 
permits. 

526.  Irrigation.  There 
are  sections  of  this  coun- 
try and  of  other  countries 
that  receive  no  rainfall  or 
such  a  limited  amount 
that  crop  production  is 
impossible  without  the 
aid  of  some  system  of 
irrigation.  The  last  few 
decades  have  seen  thou- 
sands of  square  miles  of  the  earth's  surface  that  were 
formerly  barren  made  productive  by  means  of  irrigation. 
Water  for  this  purpose  is  sometimes  obtained  from  wells 
and  springs,  but  most  of  it  comes  from  running  streams. 
In  sections  where  the  streams  become  too  low  during  the 
summer  months  the  water  is  collected  in  reservoirs  from 
which  it  is  drawn  as  needed.  In  some  cases  where  there  is 
a  plentiful  supply  of  water  it  is  merely  diverted  from  the 
river  into  canals  from  which  the  fields  are  supplied. 

Irrigation  farming  has  one  advantage  over  farming  in 
humid  climates,  namely,  that  the  farmer  has  the  water  supply 
EV.  CHEM.  —  29 


FIG.  201.  —  Laying  tile  in  ditch. 


450 


SOILS  AND   FERTILIZERS 


for  the  crops  directly  under  his  control.  Water  can  be  added 
at  the  time  it  is  needed  by  the  plants  and  in  the  right  quan- 
tity, without  dependence  upon  the  uncertainties  of  natural 
rainfall.  Under  favorable  conditions  the  expense  of  provid- 
ing the  water  is  more  than  repaid  in  the  larger  crop  pro- 
duced. 

527.  Methods  of  Irrigation.  Two  general  methods  of 
distributing  the  water  over  the  field  are  used  in  the  arid 
sections  of  this  country.  In  the  first  method  the  water 


FIG.  202.  —  Irrigation  by  furrows. 

is  flooded  over  the  ground  in  as  even  a  layer  as  possible. 
For  best  results  with  this  system  the  ground  must  be  quite 
level.  This  method  is  used  on  such  crops  as  alfalfa  or  other 
hay  crops.  On  cultivated  ground  it  is  not  so  desirable. 

The  second  method  is  more  commonly  used,  and  consists 
in  distributing  the  water  by  means  of  furrows  (Fig.  202). 
These  furrows  are  opened  at  distances  varying  with  the 
character  of  the  soil.  They  have  sufficient  fall  to  cause  the 


SOIL  WATER 


451 


water  to  run  slowly  through  them  and  so  soak  into  the  ground 
as  it  passes  along  the  furrow.  This  method  seems  to  be  the 
most  economical  of  water  and  labor  for  use  on  cultivated 
lands.  The  western  fruit  orchards  are  irrigated  in  this  way. 
528.  Irrigated  Soils  Must  be  Underdrained.  Even  in  arid 
climates,  soils  which  are  irrigated  must  be  tile  drained  after 
a  few  years  of  irrigation.  One  reason  for  this  is  that  the 


FIG.  203.  —  Irrigation  by  sprinkling. 

wonderful  yields  produced  by  the  application  of  water  have 
in  some  instances  led  to  overdoing  irrigation,  with  the  result 
that  the  soil  becomes  water-logged.  Ma*ny  areas  on  the  delta 
of  the  Nile,  for  example,  have  become  water-logged  since  the 
introduction  of  perennial  irrigation,  and  many  of  these  tracts 
are  now  being  underdrained. 

Another  reason  »why  drainage  is  necessary  in  arid  sections 
is  that  irrigation  without  drainage  brings  about  the  accumu- 
lation of  an  injurious  quantity  of  alkali  salts  near  the  surface 


452  SOILS  AND  FERTILIZERS 

of  the  soil.  The  water  dissolves  the  salts  and  brings  them 
to  the  surface  by  capillarity ;  and  then  as  the  water  evapo- 
rates the  alkalies  become  concentrated  near  the  surface. 
By  putting  in  tiles  and  using  plenty  of  water  the  excess  of 
alkalies  can  be  washed  out  of  the  soil. 

529.  Irrigation  in  Humid  Climates.  Although  there  is 
no  doubt  about  the  value  of  irrigation  in  arid  climates,  its 
usefulness  in  that  part  of  this  country  that  lies  east  of  the 
Mississippi  River  is  not  so  generally  recognized.  Eastern 
market  gardeners  find,  however,  that  it  pays  in  most  seasons 
to  do  some  irrigating.  Some  of  them  use  a  plan  much  like 
the  furrow  system,  but  many  have  adopted  a  sprinkling 
system  similar  to  the  one  shown  in  Fig.  203.  This  method 
of  applying  water  appears  to  be  very  successful  for  market 
gardens  in  the  central  and  eastern  states,  where  it  merely 
serves  to  supplement  a  naturally  good  rainfall.  Moreover, 
the  gains  in  yield  through  irrigation  of  certain  field  crops 
at  the  Wisconsin  Experiment  Station  indicate  that  even  in 
the  Middle  West  it  might  pay  to  irrigate  such  crops  on  farms 
where  water  could  be  obtained  at  little  cost. 

EXERCISES 

Ex.  324.  Fill  two  glass  tumblers  to  within  one  half  inch  of  the 
top,  one  with  a  clay  soil  and  the  other  with  a  sandy  soil.  Compact 
the  soil  by  gently  tapping  the  tumblers  on  the  desk.  Pour  water  on 
slowly  from  a  graduated  cylinder  until  it  stands  just  at  the  level  of 
the  top  of  the  soil.  Note  the  difference  in  the  amount  of  water  required 
by  the  two  soils.  The  water  absorbed  represents  the  pore  space  of 
the  soils.  Which  has  the  more  pore  space,  a  coarse-grained  or  a  fine- 
grained soil  ?  How  much  pore  space  does  a  good  loam  soil  contain  ? 

Ex.  326.  Perform  the  experiment  described  in  517.  What  is 
meant  by  film  moisture  in  soils  ?  By  ground  water  ?  By  the  water 
table  ?  At  what  depth  is  the  water  table  where  you  live  ?  How  can 
you  tell? 


SOIL  WATER 


453 


Ex.  326.  Tie  pieces  of 
cheesecloth  over  the  ends  of 
two  tall  glass  tubes,  or  two  long 
chimneys,  and  fill  one  with  a 
clayey  soil  and  the  other  with  a 
sandy  soil  .(Fig.  204).  Place 
the  lower  ends  of  the  tubes  in 
a  pan  of  water.  Does  the  water 
rise  in  the  tubes?  In  which 
will  it  rise  to  the  greater 
height?  Explain  how  evapo- 
ration from  the  surface  of  the 
soil  brings  water  up  from  be- 
low. From  what  water  in  the 
soil  do  plants  get  their  supply  ? 
Will  water  in  the  soil  move 
toward  the  plant  roots  ?  Why 
is  film  water  important  ? 

Ex.   327.     What  effect  does 


FIG.  204. — Apparatus  to  illustrate  the  capillary 
rise  of  water  in  clayey  and  sandy  soils. 


a  high  water  table  have  on  the  root  development  of  the  plant  ?  Will 
the  roots  of  the  agricultural  plants  penetrate  below  the  water  table? 
Why?  Why  does  free  water  make  the  soil  cold ?  What  effect  does  a 

wet  soil  have  on  the  plant  food?  How 
does  free  water  affect  nitrification  and 
denitrifi  cation  ? 

Ex.  328.  Grow  two  plants  in  tin 
cans,  one  of  which  has  holes  in  the  bot- 
tom while  the  other  has  not.  Keep  the 
soil  in  the  can  without  the  perforations 
saturated  with  water,  and  add  the  same 
amount  of  water  to  the  other  can.  What 
difference  do  you  note  in  plant  growth  ? 
Explain  the  various  ways  in  which  un- 
derdrainage  is  beneficial  to  soils.  Ex- 
plain how  drainage  decreases  the  danger 
of  injury  from  drought. 

20.5--p'rforat<;d  farth-         Ex.   329.     Make  three  holes  in  a  tall 
showing  how  water  leaves 

the  soil  by  drainage.  can  as  shown  in  Fig.  205.     Fill  the  can 


454 


SOILS  AND  FERTILIZERS 


with  soil  and  pour  water  on  the  top.  Through  which  hole  does  the 
water  escape?  Is  there  any  danger  of  losing  good  water  through 
drainage  ?  The  apparatus  shown  in  Fig.  206  is  convenient  in  perform- 
ing this  experiment  and  gives  condi- 
tions more  nearly  conforming  to  those 
in  a  tile-drained  field. 

Ex.  330.  How  should  you  lay  out 
a  system  of  drainage  for  your  home 
farm  ?  Is  your  farm  tile  drained  ?  In 
which  kind  of  soil  —  sandy  or  clayey 
—  should  you  lay  tile  deeper  and 
farther  apart?  How  does  the  water 
enter  the  tile  ?  Why  should  the  outlet 
of  the  tile  be  protected  ? 

Ex.  331.  In  what  sections  is  irri- 
gation most  commonly  practiced? 
Has  irrigation  farming  any  advantage 
over  the  system  which  depends  on  the 
natural  rainfall?  What  are  the  two 
more  common  methods  of  applying  the  water? 

Ex.  332.  Mix  a  little  soda  with  a  sandy  loam  soil  and  place  it  in  a 
pot.  Keep  the  pot  standing  in  a  pan  of  water.  After  some  days 
note  whether  the  soda  has  collected  at  the  top  of  the  soil.  How  do  you 
explain  it?  Why  should  irrigated  lands  be  underdrained ?  Remove 
the  pot  from  the  pan  of  water  and  pour  water  repeatedly  on  top  of 
the  soil.  Does  drainage  remove  the  alkali  ? 

Ex.  333.  What  can  you  say  about  irrigation  in  humid  climates? 
Do  any  of  the  farmers  or  gardeners  in  your  locality  use  irrigation? 
Describe  the  system  used  by  them.  Are  there  any  fields  on  your  farm 
which  could  be  irrigated  at  small  cost  ? 


FIG.  206.  —  Graham  McCall 
drainage  apparatus. 


CHAPTER  LIV 
TILLAGE 

530.  Tillage  Increases  Feeding  Ground  for  Roots.  Good 
tillage  is  the  most  efficient  means  of  assisting  nature  in  the 
conversion  of  unavailable  plant  food  into  forms  that  the 
plant  can  use.  Tillage,  in  the  sense  in  which  it  is  used  here, 
signifies  any  operation  of  stirring  and  pulverizing  the  soil 
by  means  of  plows,  harrows,  cultivators,  or  any  other  imple- 
ments, either  before  or  after  the  seed  is  sown. 

The  most  noticeable  result  of  tillage  is  that  it  makes 
the  soil  finer  by  breaking  the  large  lumps  into  smaller 
particles.  Pulverizing  the  earth  is  beneficial  in  many  ways. 
In  the  first  place,  loosening  the  soil  makes  it  easier  for  the 
plant  roots  and  root  hairs  to  penetrate  it.  Mention  has 
been  made  of  the  fact  that  all  soils  are  composed  of  particles 
of  rock  separated  by  air  spaces.  The  tender  root  hairs 
must  push  their  way  in  between  these  soil  grains,  since  it  is 
impossible  for  them  to  penetrate  the  solid  particles  them- 
selves. It  must  be  evident  that  the  more  the  soil  is  pulver- 
ized the  larger  the  number  of  the  openings  between  grains, 
and,  consequently,  the  greater  room  for' root  growth. 

Good  tillage  increases  the  amount  of  surface  exposed  to 
the  roots  by  breaking  the  large  lumps  into  small  grains ;  and 
the  more  complete  the  pulverization,  the  larger  the  area 
from  which  the  plant  can  obtain  its  food.  An  example 
will  serve  to  illustrate  what  is  meant.  A  cube  2  inches  on 
a  .side  presents  a  surface  of  24  square  inches.  If  this 

455 


456  SOILS  AND   FERTILIZERS 

cube  is  cut  once  in  each  direction,  8  cubes  are  formed,  each 
one  inch  on  a  side,  giving  a  total  of  48  square  inches  of  sur- 
face, so  that  cutting  only  once  in  each  direction  doubles 
the  amount  of  surface.  Thus,  theoretically,  a  plant  should 
be  able  to  derive  twice  as  much  food  from  the  eight  small 
cubes  as  from  the  large  one. 

531.  Tillage  Aerates  the  Soil.     One  of  the  most  advan- 
tageous results  to  be  obtained  from  tillage  is  the  aeration 
of  the  soil.    The  introduction  of  the  oxygen  of  the  air  into 
the  soil  is  of  benefit  in  many  ways.     It  makes  possible  the 
growth  of  the  plant  roots ;  it  enables  the  seeds  to  germinate ; 
it  aids  nitrification ;  and  it  prevents  denazification. 

The  oxygen  of  the  air  also  has  a  direct  chemical  action 
upon  the  mineral  matter  of  the  soil  and  tends  to  make  it 
soluble.  In  addition  it  prevents  the  formation  of  certain 
injurious  compounds,  notably  certain  ferrous  compounds. 

The  bacteria  that  enable  leguminous  plants  to  use  free 
nitrogen  are  also  dependent  upon  the  air  in  the  soil ;  for  not 
only  do  they  need  oxygen,  but  experiments  have  shown  that 
it  is  only  from  the  air  in  the  soil  that  they  can  draw  their 
supply  of  nitrogen.  It  is  necessary,  therefore,  in  order  that 
leguminous  plants  may  profit  by  the  nodule-forming  bac- 
teria, to  have  the  soil  in  such  condition  of  tilth  that  the  air 
may  freely  circulate  through  it. 

532.  Tillage    Increases    Amount    of    Available    Water. 
Tillage  not  only  increases  the  amount  of  surface  on  which 
the  plants  can  feed,  but  at  the  same  time  enlarges  the  water 
supply  by  giving  the  soil  greater  capacity  for  holding  mois- 
ture.    Attention  has  been  called  to  the  fact  that  each  soil 
grain  is  surrounded  by  a  film  of  water  which  is  called  capillary 
water  or  film  moisture.     The  plant  is  dependent  upon  this 
film  moisture  for  its  supply,  and  it  is  readily  seen  that  the 


TILLAGE  457 

\ 

amount  of  capillary  water  that  the  soil  can  retain  depends 
upon  the  aggregate  surface  area  presented  by  the  particles 
of  which  it  is  composed. 

The  following  quotation  from  King  illustrates  in  a  strik- 
ing way  the  rate  at  which  the  film  moisture  in  the  soil 
increases  as  the  soil  particles  decrease  in  size.  "  Suppose 
we  take  a  marble  exactly  one  inch  in  diameter.  It  will 
just  slip  inside  a  cube  one  inch  on  a  side,  and  will  hold  a 
film  of  water  3.1416  square  inches  in  area.  But  reduce 
the  diameters  of  the  marbles  to  one  tenth  of  an  inch,  and  at 
least  1000  of  them  will  be  required  to  fill  the  cubic  inch, 
and  their  aggregate  surface  will  be  31.416  square  inches. 
If,  however,  the  diameters  of  these  spheres  are  reduced  to  one 
hundredth  of  an  inch,  then  1,000,000  of  them  will  be  required 
to  make  a  cubic  inch,  and  their  total  surface  area  will  then 
be  314.16  square  inches.  Suppose  again  the  soil  particles 
to  have  a  diameter  of  one  thousandth  of  an  inch.  It  will 
require  1,000,000,000  of  them  to  fill  completely  the  cubic 
inch,  while  their  aggregate  surface  must  measure  3141.6 
square  inches." 

It  will  be  noted  that  the  smallest  particle  mentioned  in 
the  foregoing  paragraph  has  five  times  the  diameter  of  the 
clay  particle  (492) .  It  has  been  estimated  that  a  cubic 
foot  of  clay  has  150,000  square  feet  of  surface,  while  a  cubic 
foot  of  coarse  sand  has  40,000  square  feet  of  surface. 

533.  Tillage  to  Conserve  Moisture.  'From  what  has  been 
said  regarding  the  importance  of  water  to  the  plant  it  must 
be  apparent  that  one  of  the  chief  problems  of  agriculture 
is  to  maintain  a  proper  degree  of  moisture  in  the  soil.  It 
seldom  happens  that  a  crop  can  obtain  from  the  soil  the 
amount  of  water  necessary  for  a  maximum  yield,  and  great 
skill  is  required  to  keep  it  from  suffering  for  lack  of  moisture 


458 


SOILS  AND  FERTILIZERS 


during  the  hot  summer  period  of  scanty  rainfall.  While 
man  can  do  nothing  in  the  way  of  distributing  the  rainfall 
throughout  the  growing  season,  he  can,  by  a  judicious  use 
of  tillage  methods,  do  much  toward  saving  the  excess  of 
moisture  precipitated  in  the  early 
spring  for  the  use  of  the  plant  during 
the  drier  weather  of  the  summer.  One 
way  in  which  tillage  accomplishes  this 
end  is  by  increasing  the  capacity  of  the 
soil  for  storing  water  as  described  in 
the  preceding  paragraph.  It  must  also 
be  evident  that  the  loosening  of  the 
ground  incident  to  tillage  makes  it 
easier  for  the  rain  to  enter  the  soil  and 
tends  to  prevent  loss  by  surface  wash- 
ing, as  the  water  sinks  into  the  soil 
instead  of  running  away. 
534.  The  Earth  Mulch  to  Conserve  Moisture.  During 
dry  weather  water  is  constantly  being  evaporated  from  the 
surface  of  the  ground.  Under  ordinary  conditions,  where 
the  soil  is  somewhat  firm,  water  is  drawn  up  from  below  by 
capillary  attraction  to  replace  that  removed  by  evapora- 
tion. As  this  may  be  very  rapid  in  the  hot  dry  weather  of 
midsummer,  the  result  is  that  the  water  is  virtually  pumped 
out  of  the  soil  until  the  soil  is  too  dry  for  plant  growth. 

The  soil  under  a  board  which  has  been  lying  in  the  garden 
for  some  days  is  usually  moist,  no  matter  how  dry  the  sur- 
rounding soil  may  be,  because  the  board  has  prevented  the 
evaporation  of  the  capillary  moisture.  Gardeners  often  save 
the  moisture  of  the  soil  by  the  use  of  a  thick  mulch  of  straw 
to  prevent  evaporation.  This  method  is  not  applicable 
to  extensive  farming,  but  the  same  results  may  be  obtained 


FIG.  207.  —  The  soil 
mulch  prevents  loss  of  mois- 
ture from  the  soil. 


TILLAGE  459 

by  the  use  of  the  earth  mulch,  which  is  simply  a  layer  of 
soil  two  or  three  inches  deep  so  dry  and  loose  that  it  cannot 
take  up  the  capillary  water  from  the  soil  beneath  it.  To 
make  an  effective  earth  mulch  the  cultivation  should  be 
shallow  and  frequent,  the  aim  being  to  make  the  layer  as 
dry  as  possible.  A  rain,  of  course,  will  again  compact  the 
loose  earth  and  renew  capillarity,  so  that  cultivation  should 
be  repeated  as  soon  as  possible  after  a  rain.  Even  in  absence 
of  rain  the  mulch  will  sooner  or  later  become  compact  if 
left  too  long  without  stirring.  A  mulch  about  three  inches 
deep  has  been  found  to  be  most  effective  in  conserving 
moisture. 

The  surface  of  irrigated  soils  should  be  cultivated  as  soon 
after  each  application  of  water  as  possible,  so  that  an  earth 
mulch  may  be  formed 
and  the  water  retained. 
This  practice  results  in 
a  great  saving  in  the 
amount  of  water  that 
has  been  applied. 

535.    Early      Spring 
Plowing    to    Conserve 

Moisture.      Plowing  the      FIG.  208.  — Large  amounts  of  water  are  lost 

ground  very  early  in  the 

spring  is  a  desirable  practice,  for  there,  is  no  other  season 
when  tillage  is  so  effective  in  conserving  the  moisture  of  the 
soil.  King  reports  one  experiment  in  which  early-plowed 
ground  seven  days  after  plowing  contained  an  amount  of 
water  equal  to  1.75  acre  inches  in  excess  of  an  adjoining 
plot  which  was  not  plowed.  An  acre  inch  of  water  is  the 
amount  of  water  that  would  make  a  layer  an  inch  deep  over 
an  acre  of  ground.  An  experiment  on  early  and  late  plowing 


430  SOILS  AND  IERTILIZERS 

for  corn  in  Ohio  showed  that  the  moisture  content  of  the 
early-plowed  plots  was  higher  throughout  the  season  than 
that  of  the  late-plowed  plots.  It  showed  also  that  the 
available  nitrogen  was  much  higher  in  the  early-plowed 
plot  and  that  the  yield  of  corn  was  greater.  Therefore  the 
soil  should  be  stirred  as  early  in  spring  as  possible  without 
injury  to  its  texture,  either  by  plowing  or  by  the  use  of  some 
form  of  cultivator  or  harrow. 

536.  Fall  plowing  as  well  as  spring  plowing  increases 
the  water  supply  of  the  soil,  because  it  leaves  the  ground 
with  a  loose  uneven  surface,  in  which  condition  it  more 
readily  absorbs  the  water  of  the  winter  rains.  An  experi- 
ment reported  from  Wisconsin  shows  that  a  plot  plowed 
in  the  fall  contained  1.15  inches  more  water  than  an  adjacent 
plot  not  so  plowed.  Many  soils  in  the  northern  states  are 
improved  by  fall  plowing,  because  the  freezing  and  thawing 
brings  about  disintegration  of  the  clods  and  leaves  the  soil 
in  better  tilth.  The  greatest  advantage  of  fall  plowing,  how- 
ever, is  that  it  decreases  the  amount  of  plowing  that  must 
be  done  during  the  rush  of  spring  work.  Soils  that  are  sub- 
ject to  washing  cannot  safely  be  plowed  in  the  fall. 

637.  Tillage  to  Destroy  Weeds.  Weeds  should  not  be 
allowed  to  grow,  because  they  rob  the  crop  of  the  moisture 
and  plant  food  that  it  needs.  Since  weeds  are  usually 
broad-leaved,  vigorous  plants  that  transpire  large  quantities 
of  water,  and  since  there  is  seldom  water  to  spare  in  the 
soil,  weeds  are  injurious  to  the  growing  crop. 

While  it  is  probable  that  weeds  work  the  greatest  injury 
to  the  crop  by  depriving  it  of  water,  they  also  rob  it  of 
mineral  food.  Some  farmers  argue  that  if  the  plants  remain 
on  the  ground  they  remove  no  plant  food.  It  must  be 
remembered,  however,  that  they  use  that  portion  of  the 


TILLAGE  461 

plant  food  that  would  be  available  to  the  crop  and  that 
the  weeds  must  decay  before  this  food  is  again  rendered 
available.  In  so  far  as  any  one  crop  is  concerned  the  plant 
food  is  as  completely  removed  by  a  growth  of  weeds  imme- 
diately preceding  it  as  it  would  be  if  it  were  actually  taken 
from  the  field.  In  an  experiment  in  New  Hampshire  corn 
was  grown  with  and  without  cultivation,  so  that  in  one  plot 


FIG.  209.  —  A  well-prepared  seed  bed  is  important  in  the  production  of  large  crops. 

the  weeds  were  allowed  to  grow,  while  in  the  other  the  weeds 
were  all  destroyed.  The  first  plot  produced  only  17  bushels 
to  the  acre,  while  the  cultivated  plot  yielded  80  bushels. 

The  destruction  of  weeds  was  formerly  regarded  as  the 
only  reason  for  tillage  after  seeding.  It  is  now  known, 
however,  that  stirring  the  soil  has  a  distinct  value  in  itself. 
If  the  farmer  tills  his  soil,  so  as  to  reap  the  maximum  benefits 
of  this  process,  he  will  have  no  need  to  worry  about  the  weeds. 

538.  Dry  Farming.  It  has  been  estimated  that  one 
half  of  this  country  has  a  rainfall  of  less  than  twenty  inches. 


462 


SOILS  AND   FERTILIZERS 


FIG.  210.  —  Barley  grown  three  years  in 
succession  in  a  dry  fanning  district.  Yield 
5.33  bushels  per  acre. 


Such  a  rainfall  is  not  sufficient  to  produce  a  good  crop 
each  year.  In  some  of  these  semi-arid  sections  the  land  is 

, ; ,    so  located  that  it  can  be 

irrigated,  and  it  is  being 
rapidly  reclaimed  by  the 
irrigation  projects  of  the 
national  government  as 
well  as  by  those  of  pri- 
vate enterprise. 

Much  more  of  the 
land  in  these  semi-arid 
sections,  however,  is  be- 
yond the  reach  of  irri- 
gation, and  must  be 
handled  in  an  entirely 
different  manner  if  it  is  to  produce  profitable  crops.  On 
some  of  these  lands  dry  farming  is  followed.  This  is  prac- 
ticable on  land  receiv- 
ing an  annual  rainfall 
of  12  to  14  inches  or 
more,  and  consists  in 
utilizing  the  moisture 
of  two  years  to  produce 
a  crop,  instead  of  trying 
to  grow  one  each  year. 
It  is  a  broad  application 
of  the  earth  mulch. 
In  dry  farming  a  crop 

is      produced     in      each         FIG.  211.  — Barley  grown  after  fallow  on  land 

field  once  in  two  years,  adjacent toFig' 2I0'  Yield31-27 busnels  Peracre- 
so  that  a  farmer  who,  for  example,  owns  320  acres  has  crops 
growing  on  160  acres  but  nothing  growing  on  the  other  160 


TILLAGE  463 

acres.  Immediately  after  a  crop  is  harvested  the  ground  is 
plowed  and  harrowed  to  produce  an  earth  mulch  which  is 
maintained  by  thorough  cultivation  for  the  remainder  of 
that  year  and  all  through  the  second  year.  The  principle  of 
the  mulch  is  carried  still  farther,  for  the  ground  after  seeding, 
and  even  after  the  crop  is  up,  is  harrowed  as  long  as  it  can 
be  done  without  injury  to  the  growing  crop. 

This  system  of  tillage  permits  all  the  rain  water  to 
soak  into  the  soil  and  prevents  its  subsequent  evaporation, 
a  condition  which  is  very  necessary  because  the  dry  air  and 
winds  of  the  semi-arid  regions  cause  rapid  evaporation.  The 
soils  in  these  regions  are  high  in  available  plant  food  because 
very  little  of  it  has  been  leached  out,  and  the  only  requisite 
for  a  good  crop  is  an  adequate  supply  of  water. 

Some  of  these  soils  settle  so  slowly  after  plowing  that  a 
special  implement  known  as  the  subsurface  packer  has  been 
invented  for  use  on  them.  This  implement  packs  the  soil 
below  without  destroying  the  loose  condition  of  the  surface. 
In  this  way  capillary  connection  is  renewed  between  the 
plowed  soil  and  that  beneath,  while  evaporation  from  the 
surface  is  prevented  by  the  mulch. 

539.  Summer  Fallowing.  A  practice  similar  to  dry  farm- 
ing was  formerly  followed  in  humid  climates  and  is  still 
advocated  by  some  people.  This  practice,  which  is  knov/n 
as  summer  fallowing,  consists  in  allowing  the  field  to  go 
through  one  summer  without  growing  a  crop,  the  surface 
of  the  soil  being  frequently  cultivated  to  produce  a  mulch. 

This  method  came  into  use  at  a  time  when  the  tillage 
implements  were  very  crude  and  it  was  possible  to  control 
the  weeds  in  no  other  way.  The  crop  following  a  summer 
fallow  is  always  larger  than  it  would  be  otherwise,  but  in 
sections  with  an  annual  rainfall  of  over  thirty  inches,  dis- 


464  SOILS  AND  FERTILIZERS 

tributed  throughout  the  year,  the  increase  of  crop  seldom 
pays  for  the  loss  of  a  crop  during  the  fallow  year.  There 
is  also  danger  in  this  method  of  excessive  loss  of  nitrogen 
by  leaching.  In  an  experiment  at  the  New  York  Experi- 
ment Station  over  300  pounds  of  nitrogen  were  lost  in  a  year 
in  the  drainage  of  water  from  an  acre  of  fallow  ground,  an 
amount  equal  to  that  removed  by  four  50  bushel  crops  of 
corn.  No  nitrogen  was  lost  from  an  adjoining  plot  on 
which  grass  was  growing,  because  the  plants  utilized  the 
nitrates  as  fast  as  they  were  formed. 

540.  Short  Fallows  Desirable.  Although  the  long  sum- 
mer fallow  is  to  be  recommended  only  when  the  soil  has 
been  abused  and  has  become  so  foul  with  weeds  that  no 
other  method  will  remove  them,  frequent  use  should  be  made 
between  crops  of  the  short  fallow.  It  will  be  found  advan- 
tageous in  many  instances  to  plow  the  land  immediately 
after  the  removal  of  one  crop  and  keep  it  well  stirred  until 
the  planting  of  the  next  plot.  By  this  means  loss  of  moisture 
from  the  soil  is  prevented,  the  decomposition  of  the  organic 
matter  is  hastened,  and  a  large  supply  of  available  plant 

food  is  prepared  for 
the  succeeding  crop. 
This  method  is  es- 

W        ^^ygjjjjjj         pecially  to  be  recom- 
mended in  preparation 

.i^^Sffr-  *-•  -~.      for  fall-sefed  CT°PS  in 

sections  of  scanty  sum- 
mer rainfall. 


F,0.212.-Plowmgina,eOrient. 

plow  is  one  of  the  oldest 

tillage    implements,  its  use   antedating   history.     From  a 
crooked  stick  (Fig.  212)  drawn  by  an  ox,  a  donkey,  or  even 


TILLAGE 


465 


a  slave,  the  plow  has  developed  into  the  steel  mold- 
board  plow  (Fig.  213)  of  to-day.  There  are  many  kinds 
of  plows,  a  kind  for  every  purpose,  the  principal  differ- 
ences in  them  being  the  shape  of  the  moldboard.  The 


MOLDBOARD 
SHARE 

POINT 


BEAM 


FIG.  213.  —  General  purpose  plow. 


breaking  plow  (Fig.  214)  has  a  long  moldboard  with  a 
slight  curve  that  turns  the  sod  without  breaking  it.  The 
stubble  plow  has  a  steep  moldboard  with  a  sharp,  bold 


LTEIR 


FIG.  214.  —  Breaking  plow. 


outward  curve  at  its  upper  extremity,  which  gives  the 
furrow  slice  a  twist,  causing  it  to  break  and  crumble  as 
it  falls.  There  is  a  plow  (Fig.  215),  that  has  a  revolving 
steel  disk  in  place  of  the  moldboard.  The  advantage 
EV.  CHEM.  —  30 


466 


SOILS  AND  FERTILIZERS 


claimed  for  this  plow  is  that  it  overcomes  the  danger  of 
developing  a  hardpan,  which  may  happen  when  the  land 
is  plowed  repeatedly  at  the  same  depth  with  the  ordinary 


FIG.  215.  — Disk  plow. 

plow.     The  disk  plow  does  not  work  well  in  heavy  clay 

soils,  but  is  better  adapted  to  lighter  soils. 

542.   Plowing  is  the  most   laborious,   but  at  the  same 

time  the  most  effective,  tillage  operation,  and   should  be 

so  conducted  as  to 
leave  the  least  pos- 
sible amount  of  work 
for  the  tillage  im- 
plements that  fol- 
low. The  plowing 
should  completely 
cover  all  vegetation 

and  manure  and  incorporate  it  as  completely  as  possible 

with  the  soil. 
The  depth  to  plow  depends  upon  the  soil,  the  climate,  the 

crop  to  be  grown,  and  the  time  of  the  year.     In  general  it  may 


FlG.  216.  —  Subsoil  plow. 


TILLAGE 


467 


be  said  that  light  sandy  soils  should  be  plowed  from  five  to  six 
inches,  while  clay  soils  should  be  plowed  eight  or  nine  inches 
deep.  In  case  of  a  clay  soil  that  has  previously  had  shallow 
plowing,  the  soil  should  be  gradually  deepened  by  setting 
the  plow  an  inch  deeper  each  time  until  the  desired  depth 
has  been  reached. 
,  Plowing  deeper 
than  eight  to  ten 
inches  requires  more 
power  and  raises 
the  question  as  to 
how  deep  the  soil 
may  be  plowed  with 
profit.  Special  deep- 
tillage  implements 
(Fig.  217)  have 
lately  been  devised 
that  will  turn  the 
soil  to  a  depth  of 
from  twelve  to  four- 
teen inches ;  but 
since  they  require 
nearly  twice  the 
power  of  an  ordi- 
nary plow  running  FIG.  217.  —  Deep-tillage  machine. 

nine  or  ten  inches,  it  remains  to  be  seen  whether  the  extra 
labor  outlay  is  profitable.  The  subsoil  plow  (Fig.  216), 
which  follows  after  the  ordinary  plow  and  loosens  the  subsoil 
in  the  bottom  of  the  furrow;  has  been  known  for  some  years 
but  never  has  been  popular ;  and  its  use  is  seldom  advocated. 
One  of  the  most  difficult  things  to  judge  is  the  proper 
time  to  plow  clay  soils.  This  can  be  learned  only  by  experi- 


468  SOILS  AND  FERTILIZERS 

ence.  If  the  soil  is  too  wet,  the  working  of  it  puddles  the 
clay  so  that  upon  drying  the  soil  is  left  hard  and  lumpy.  If 
the  soil  is  too  dry  it  will  be  so  hard  that  the  draft  on  the  plow 
is  very  great  and  the  furrow  slice  breaks  into  large,  hard 
clods.  Plowed  at  the  right  time,  the  soil  will  crumble 
into  a  loose  mass  and  be  left  in  good  tilth. 

543.   Harrows    and    Harrowing.     As    soon    as    possible 
after  the  ground  is  plowed  the  soil  should  be  completely 


FIG.  218.  —  Spike-tooth  harrow. 

pulverized  by  means  of  the  harrow.  In  this  way  a  better 
seed  bed  is  prepared,  and  a  soil  mulch  is  formed  on  the  sur- 
face to  conserve  moisture.  Many  farmers  delay  the  har- 
rowing too  long,  with  the  result  that  the  soil  becomes  dry 
and  does  not  readily  pulverize.  In  case  a  crust  forms  on 
the  ground  before  planting  it  should  be  harrowed  again. 
In  fact,  the  modern  practice  is  to  harrow  the  ground  even 
after  the  crop  is  up,  especially  in  the  case  of  corn.  There 
is  no  more  effective  and  economical  method  of  destroying 
weeds  than  by  these  repeated  harrowings  in  the  spring. 
For  use  on  light  soils  the  harrow  is  sometimes  replaced  by 
the  weeder. 


TILLAGE 


469 


The  most  common  form  of  harrow  is  the  spike-tooth  har- 
row (Fig.  218)  with  either  the  wooden  or  metal  frame.  A 
lever  is  commonly  attached  so  that  the  spikes  may  be  set  at 
different  angles  and 
thus  be  made  to  go  at 
varying  depths. 

The  spring-tooth 
harrow  (Fig.  219)  is 
also  used  to  pulverize 
the  top  soil.  It  is  rec- 
ommended for  stony 
ground,  since  the  teeth 
can  spring  back  and 

.  FIG.  219.  — Spring-tooth  harrow. 

release  themselves 

when  they  catch  upon  an  obstruction.  It  is  also  some- 
times used  to  cultivate  alfalfa  and  other  growing  crops  in  the 
spring.  The  Acme  harrow  (Fig.  220)  consists  of  a  row  of 


FIG.  220.  —  Acme  harrow. 


curved  knife-teeth  and  cuts  and  pulverizes  the  soil  in  such 
a  way  as  to  prepare  a  good  seed  bed. 

The  disk  harrow  (Fig.  221)  is  one  of  the  most  useful  im- 
plements of  the  farm.     It  is  effective  for  loosening  and  pul- 


470 


SOILS  AND  FERTILIZERS 


FIG.  221.  —  Disk  harrow. 


verizing  the  soil ;  for  as  the  disks  cut  the  clods  they  also  mix 
the  surface  soil.  The  two  sets  of  disks  are  set  at  an  angle  and 
push  the  dirt  away  from  the  center;  hence  it  is  customary 

in  disking  the 
ground  to  lap  one 
half  the  distance 
in  order  that  the 
ground  may  be 
left  more  level. 
The  disk  harrow 
is  often  used  to 
loosen  the  ground 
before  plowing  as 
well  as  to  cut 
cornstalks  and 
rubbish  to  make  them  more  easily  covered.  The  disk  harrow 
is  often  used  in  place  of  the  plow  in  preparing  the  ground 
in  the  spring  for  oats  when  they  follow  corn  in  rotation. 
When  spring  plowing  is  delayed,  it  is  often  advisable  to  go 
over  the  ground  with 
the  disk  harrow  so  as 
to  loosen  the  surface 
and  prevent  evapora- 
tion. 

544.  Use  of  the  Roll- 
er. It  is  seldom  neces- 
sary to  use  the  roller 
(Fig.  222)  after  spring 
plowing  in  humid  cli- 
mates. If  the  soil  is  moist  or  the  plowing  is  followed  by 
rains,  a  good  contact  is  formed  between  the  plowed  ground 
and  the  subsoil,  and  capillarity  is  renewed.  In  dry  weather 


FIG.  222.  —  Roller. 


TILLAGE 


471 


or  in  case  much  organic  matter  is  plowed  under,  the  heavy 
roller  may  be  useful  in  pressing  the  plowed  ground  down 
upon  the  soil  beneath. 
As  a  means  of  break- 
ing the  clods  and  pul- 
verizing the  soil  the 
roller  is  not  very  effi- 
cient. When  used  it 
should  be  followed  by 
the  harrow  to  restore 
the  surface  mulch. 

The  plank  drag  (Fig. 
223)  is  frequently  used  FlG'  223'  ~  plank  drag" 

by  gardeners  to  break  the  clods  and  make  the  soil  fine. 

545.  Intertillage.  Some  crops,  like  corn,  are  intertilled, 
or  cultivated  between  the  rows,  during  at  least  a  part 
of  the  growing  season.  Many  implements  have  been 

devised  for  this  pur- 
pose, the  kinds  vary- 
ing from  the  one-horse 
cultivator  to  the  two- 
row  riding  corn  culti- 
vator (Fig.  224).  The 
cultivating  teeth  of 
these  implements  are 
of  all  sizes  and  forms. 
The  cultivation  should 

FIG.  224.  -Two-row  riding  corn  cultivator.  ^  fallow.       It  should 

be  frequent  enough  to  maintain  a  good  soil  mulch.  The 
scil  should  be  left  level,  and  all  ridging  should  be  avoided, 
as  uneven  ground  exposes  more  surface  for  evaporation  of 
water. 


472  SOILS  AND  FERTILIZERS 

EXERCISES 

Ex.  334.  Describe  the  effect  of  tillage  in  pulverizing  the  soil.  Why 
can  plants  obtain  more  food  from  a  fine-grained  soil  ?  In  what  ways 
is  aeration  of  the  soil  by  means  of  tillage  beneficial  ? 

Ex.  335.  Explain  how  tillage  and  pulverizing  increase  the  water- 
holding  capacity  of  soils. 

Ex.  336.  Fill  two  cans  to  within  one  inch  of  the  top  with  moist 
soil.  On  top  of  the  soil  in  one  can  place  one  half  inch  of  fine  dry  earth. 
Place  the  cans  on  opposite  pans  of  a  balance  and  add  weights  or  sand 
to  the  pan  on  the  lighter  side  until  the  indicator  of  the  balance  is  at 
zero.  Note  which  can  loses  moisture  more  quickly.  Explain.  Will  a 
layer  of  straw  do  the  same  thing  ?  How  is  the  soil  mulch  prepared 
and  maintained?  Explain  the  effect  of  late  fall  plowing  and  early 
spring  plowing  upon  the  moisture  content  of  the  soil.  Why  should 
the  surface  of  irrigated  soil  be  cultivated  ? 

Ex.  337.  Why  should  all  weeds  be  destroyed?  How  do  they 
affect  the  water  supply  of  the  plant  ?  The  food  supply  ?  The  yield  of 
the  crops  ?  Would  it  pay  to  cultivate  if  there  were  no  weeds  ? 

Ex.  338.  Under  what  climatic  conditions  is  dry  farming  practiced  ? 
How  is  it  conducted  ?  Explain  use  of  the  subsurface  packer. 

Ex.  339.  What  is  meant  by  summer  fallowing?  Is  it  advisable 
in  humid  climates?  What  is  the  danger  connected  with  it?  Ex- 
plain how  short  fallows  might  be  used  to  advantage. 

Ex.  340.  Compare  the  breaking  plow  and  the  stubble  plow.  How 
does  the  disk  plow  work?  Why  should  the  plow  be  made  to  pulverize 
the  soil  as  much  as  possible?  What  determines  the  depth  to  plow? 
How  can  you  deepen  a  clay  soil  which  has  always  been  shallow  plowed  ? 
Why  is  deep  plowing  more  expensive  than  shallow  plowing?  What 
is  a  good  depth  to  plow  clay  soils?  What  is  meant  by  subsoil  plow- 
ing ?  Why  is  it  difficult  to  tell  when  to  plow  stiff  clay  soils  ? 

Ex.  341.  What  operation  usually  follows  plowing?  Name  dif- 
ferent kinds  of  harrows  used  in  your  neighborhood.  Note  all  the 
different  uses  made  of  the  disk  harrow. 

Ex.  342.  Is  it  often  advisable  to  use  the  roller  ?  What  should  be 
done  immediately  after  rolling?  Explain  the  use  of  the  plank  drag. 
Describe  different  kinds  of  cultivators  for  corn.  State  some  general 
rules  for  jntertillage.  Why  is  level  cultivation  best  ? 


CHAPTER  LV 
KEEPING   THE   SOIL   SWEET 

546.  Soil    Acidity.     Many    soils    fail    to    produce    good 
crops   because  they  are   acid,   or   sour.     It  was   formerly 
supposed  that  only  low-lying  or  marshy  soils  ever  became 
sour,  but  it  is  now  known  that  there  are  large  areas  of  up- 
lands where  an  acid  condition  of  the  soil  exists.     These 
acid  soils  are  widely  distributed  and  are  found  in  all  parts 
of  the  world,  but  especially  in  humid  climates. 

547.  Cause  of  Acidity.     Soil  acidity  is  due  to  a  lack  of 
limestone  (calcium  carbonate)  in  the  soil.     Acids  are  con- 
stantly being  formed  in  the  soil,  and  unless  these  acids  are 
neutralized  they  cause  the  soil  to  become  sour.     When  the 
soil    contains   an   abundance    of   calcium   carbonate   these 
acids  are  neutralized  as  rapidly  as  they  are  formed,  but 
in  this  action,  of  course,  some  of  the  carbonate  itself  is 
destroyed.     The  more  thorough  the  cultivation  the  more 
rapidly  organic  matter  is  oxidized  and  acid  substances  are 
formed,  and  consequently  the  greater  is  the  destruction  of 
the  limestone  in  the  soil.     Moreover,  the  growing  crop  uses 
some  of  the  calcium  of  the  limestone  in  making  its  growth 
and  thus  removes  it  from  the  soil.     Manures  and  fertilizers 
also  temporarily  produce  acidity  of  the  soil  and  thus  destroy 
the  limestone,  and,  finally,  large  quantities  of  calcium  car- 
bonate are  removed  from  the  soil  in  the  drainage  water. 
The  carbonic  acid  of  the  soil  water  acts  upon  the  limestone, 

473 


474 


SOILS  AND  FERTILIZERS 


forming  calcium  bicarbonate  (119),  as  is  shown  by  the  hard- 
ness of  the  drainage  water  in  limestone  countries. 

548.  Soil  acidity  is  injurious  to  most  of  the  crops  that 
are  grown  in  ordinary  farming  or  gardening.     Clover,  alfalfa, 
and  other  important  legumes  are  particularly  sensitive  to 
the  lack  of  limestone  in  the  soil.     This  is  due  in  part  to  the 

fact  that  these  legumes 
use  comparatively  large 
quantities  of  calcium 
during  their  growth, 
but  apparently  it  is 
true  also  that  the  bac- 
teria that  enable  these 
legumes  to  fix  the  free 
nitrogen  of  the  air  do 
not  thrive  in  a  sour 
soil .  At  any  rate  these 
legumes  will  not  grow 
in  acid  soils,  and  ordi- 
nary farming  cannot  be  successful  without  the  growth  of 
legumes  to  furnish  a  cheap  supply  of  nitrogen  by  the  fixa- 
tion of  that  element  from  the  atmosphere. 

549.  Acidity  Prevents  Nitrification.     It  has  been  shown 
that  the  process  of  nitrification  in  the  soil  is  essential  to  the 
successful  production  of  the  common  field  crops.     One  of 
the  requirements  for  nitrification  is  that  there  is  present 
in  the  soil  some  basic  substance  with  which  the  nitrous 
acid  may  unite  as  rapidly  as  it  is  formed.     Limestone  is  the 
most  important  basic  substance  in  the  soil,  and  when  it  is 
exhausted  the  soil  becomes  acid  and  nitrification  is  no  longer 
possible.     The  bacteria  that  cause  denitrificatioh,  on  the 
other  hand,  seem  not  to  be  sensitive  to  acidity ;  hence  this 


FIG.  225.  —  Effect  of  limestone  on  growth  of 
sweet  clover.  The  strip  in  center  received  no 
limestone. 


KEEPING  THE  SOIL  SWEET  475 

injurious  action  is  likely  to  be  accelerated  in  sour  soils.  It 
is  of  utmost  importance,  therefore,  that  acidity  of  the  soil 
should  be  corrected. 

550.  How  to  Recognize  a  Sour  Soil.    The  character  of 
the  vegetation  gives  some  indication  as  to  whether  or  not 
the  soil  is  acid.    Where  such  plants  as  common  sorrel, 
horsetail,  rushes,  and  mosses  take  possession  of  the  land, 
it  is  a  strong  indication  of  acidity,  because  these  plants 
can  withstand  a  large  amount  of  acid  and  hence  persist 
after  the  soil  has  become  too  sour  for  the  growth  of  more 
desirable  plants.     Sometimes  an  acid  soil  becomes  so  covered 
with  sorrel  as  to  give  a  reddish  tinge  to  the  entire  field. 

The  persistent  failure  of  clover  is  an  indication  of  soil 
acidity,  while  a  good  growth  of  clover  shows  that  the  soil 
contains  sufficient  limestone.  On  acid  soils  the  clover  fre- 
quently starts  growth  with  promise  in  the  early  spring, 
but  later  becomes  sickly  in  appearance  and  finally  dies  out 
completely.  Such  behavior  is  practically  always  due  to  a 
sour  condition  of  the  soil. 

551.  The   Litmus   Test   for   Acidity.     One   of   the   best 
methods  of  testing  the  soil  for  acidity  is  known  as  the  litmus 
paper  test,     In  the  laboratory  the  test  may  be  applied  by 
moistening  the  soil  with  distilled  water  and  placing  a  piece 
of  blue  litmus  paper  on  the  moist  mass.     If  the  litmus  paper 
turns  pink  within  ten  minutes,  the  soil  is  acid. 

Owing  to  the  difficulty  of  obtaining  pure  distilled  water 
it  is  generally  best  to  make  the  test  on  the  moist  soil  direct 
from  the  field.  A  handful  of  the  soil  is  pressed  into  a  ball, 
which  is  then  broken  in  two,  and  the  litmus  paper  is  placed 
between  the  two  halves  of  the  ball.  After  ten  minutes  the 
paper  is  examined. 

Care  should  be  exercised  hi  using  the  litmus  paper,  as 


476 


SOILS  AND  FERTILIZERS 


fit"\  WF» 


the  perspiration  of  the  hands  is  usually  acid  in  reaction. 
The  safest  way  is  to  use  a  pair  of  small  forceps  in  handling 
the  paper.  Only  a  sensitive  litmus  paper,  such  as  is  used 
in  the  chemical  laboratory,  should  be  employed  in  making 
the  test.  The  cheap  blue  litmus  papers  so  often  found  in 
the  drug  stores  are  strongly  alkaline  and  will  not  change 
color  even  in  soil  which  is  sour  enough  to  prevent  entirely 
the  growth  of  clover. 

552.  The  Truog  test  for  acidity  consists  in  mixing  the 
soil  to  be  tested  with  a  small  quantity  of  calcium  chloride 
and  a  very  little  zinc  sulphide.    Water  is  added  and  the 

mixture  is  heated  to 
boiling.  A  strip  of  lead 
acetate  paper  is  held 
over  the  mouth  of  the 
flask  for  two  minutes 
while  the  boiling  pro- 
ceeds. If  the  soil  is 
acid  it  reacts  on  the 
zinc  sulphide  and  forms 
hydrogen  sulphide, 
which  darkens  the  lead 
acetate  paper  (87).  If 
no  acid  is  present  in 
the  soil  no  darkening 
of  the  paper  will  occur.  When  the  directions  are  carefully 
followed  the  color  of  the  lead  paper  gives  some  idea  of  the 
degree  of  acidity  in  the  soil.  A  small  outfit  including  an 
alcohol  lamp  for  heating  water  so  that  the  test  may  be  used 
in  the  field  is  now  on  the  market  (Fig.  226) . 

553.  Hydrochloric  acid  is  used  to  show  the  presence  of 
an  abundance  of  limestone  in  the  soil.    A  handful  of  soil 


FIG.  226.  —  Apparatus  for  Truog  test. 


KEEPING  THE   SOIL  SWEET 


477 


is  pressed  into  a  ball,  and  then  a  depression  is  made  in  it  to 
hold  a  little  dilute  hydrochloric  acid.  If  a  considerable 
amount  of  limestone  is  present,  it  will  be  shown  by  efferves- 
cence caused  by  the  action  of  the  acid  on  the  calcium  car- 
bonate. A  decided  effervescence  indicates  that  the  soil 
contains  sufficient  limestone  for  all  purposes.  The  small 
amount  of  air  which  is  forced  out  of  the  soil  by  the  liquid 
must  not  be  mistaken  for  effervescence  from  the  carbonates. 
This  test  is  of  limited  application  only,  since  a  soil  may  be 
neutral  in  reaction  and  able  to  produce  clover  and  yet  not 
contain  enough  carbonate  to  give  a  noticeable  evolution  of 
carbon  dioxide. 

554.  Correcting  Acidity.  When  any  of  the  tests  indicate 
that  the  soil  is  sour,  it  is  necessary  to  add  to  it  some  substance 
that  will  neutralize  and  thus  destroy  the  acid .  The  cheapest 
material  that  can  be 
used  for  this  purpose 
is  ordinary  limestone. 
The  stone  is  pulverized 
by  crushers  (Fig.  227) 
and  rollers  until  it  is 
fine  enough  to  be  ap- 
plied with  a  lime  drill. 
A  powder  that  will  all 
pass  through  a  sieve 
having  ten  meshes  to 
the  linear  inch  is  suf- 
ficiently fine,  although 
the  finer  the  stone  the  quicker  it  will  act  on  the  soil. 

The  ordinary  application  of  ground  limestone  to  acid 
soils  is  two  tons  to  the  acre.  It  is  best  applied  by  means  of 
especially  devised  lime  spreaders  (Fig.  228)  which  can  be  set 


FIG.  227.  —  A  small  portable  pulverizer  for 
'  grinding  limestone. 


478 


SOILS  AND  FERTILIZERS 


to  distribute  from  five  hundred  pounds  to  four  or  five  tons 
to  the  acre.  A  manure  spreader  may  be  used  by  covering 
the  bottom  with  straw  and  placing  the  powdered  limestone  on 
top,  or  a  skilled  worker  may  even  spread  it  from  the  wagon 


FIG.  228.  —  Applying  ground  limestone  with  a  spreader. 

by  means  of  a  shovel.  If  much  limestone  is  to  be  used, 
the  special  spreader  will  soon  pay  for  itself. 

It  sometimes  happens  that  a  farm  that  has  an  acid  soil 
also  has  outcroppings  of  limestone.  Small  portable  lime- 
stone crushers  are  on  the  market  at  a  low  price,  which  make 
it  possible  under  such  conditions  for  the  farmer  to  crush  his 
own  limestone  at  a  small  expense.  It  is  to  be  noted  that 
even  in  limestone  sections  acid  areas  are  frequently  found, 
especially  on  the  high  lands  that  have  been  under  cultiva- 
tion for  a  long  period. 

555.  Other  Forms  of  Lime.  Although  under  ordinary 
circumstances  ground  limestone  is  the  cheapest  and  best 
material  to  use  for  correcting  the  acidity  of  soils,  it  may 


KEEPING  THE  SOIL  SWEET  479 

happen  that  the  land  is  so  far  removed  from  any  source 
of  limestone  that  the  freight  charges  are  excessive.  In  such 
a  case  it  might  be  more  economical  to  use  quicklime  (CaO) 
in  place  of  the  limestone.  In  burning  100  pounds  of  calcium 
carbonate  56  pounds  of  lime  are  produced ;  but  the  latter  has 
the  same  power  to  neutralize  acids  as  the  former.  Thus  it 
will  be  seen  that  not  much  more  than  one  ton  of  quicklime 
will  do  the  same  work  as  two  tons  of  limestone. 

Hydrated  lime,  which  is  merely  another  name  for  slaked 
lime  (Ca(OH)2),  is  often  recommended  for  use  on  the  soil. 
It  is  effective  in  neutralizing  acidity,  but  is  usually  too  high 
in  price  for  that  purpose. 

Air-slaked  lime  (115)  is  formed  when  quicklime  is  exposed 
to  the  air.  If  it  stands  for  a  long  time  the  calcium  is  all 
converted  into  the  carbonate,  with  the  result  that  the  ma- 
terial is  practically  the  same  as  very  finely  ground  limestone. 
One  ton  of  quicklime  is  equivalent  in  neutralizing  power 
to  2640  pounds  of  hydrated  lime,  or  3570  pounds  of  carbonate 
of  lime;  and  these  relations  should  be  kept  in  mind  when 
determining  which  substance  is  most  economical  to  buy. 

556.  Marl.     In  many  places  beds  of  marl  of  considerable 
size  are  found.    Most  of  the  marls  are  formed  from  shell 
deposits,  and  consist  of  carbonate  of  lime  of  more  or  less 
purity.    As  marl  is  practically  the  same  as  ground  lime- 
stone, it  has  the  same  effect  upon  the  soil,  and  is  a  convenient 
form  in  which  to  use  lime  when  obtainable  at  reasonable 
cost.     Some   of  the   European/  marls   contain   appreciable 
quantities  of  potash  and  phosphoric  acid  as  well,  but  the 
American  marls  are  of  value  only  for  the  lime  they  contain. 

557.  When  to  Apply  Limestone.    The  principal  reason 
for  using  limestone  or  the  other  forms  of  lime  is  to  enable 
the  soil  to  produce  clover  or  other  legumes;   consequently 


480  SOILS  AND  FERTILIZERS 

the  limestone  should  be  used  far  enough  in  advance  of  the 
leguminous  crop  to  insure  the  neutralizing  of  the  acidity 
of  the  soil  before  the  legume  is  planted.  If  corn  is  grown 
in  the  rotation,  it  is  advisable  to  spread  the  limestone  on 
the  ground  immediately  after  plowing,  and  to  harrow  it  in. 
In  this  way  the  limestone  is  thoroughly  mixed  with  the 
soil  and  has  time  to  destroy  the  acids  before  the  legume 
is  seeded. 

558.  Field  Test  with  Limestone.     The  tests  for  acidity 
already  described  are  all  good  in  their  way ;  but  the  impor- 
tance of  having  right  conditions  for  the  growth  of  clover  is 
so  great  that  a  practical  test  of  limestone  in  the  field  should 
be  made  in  every  case  where  the  growth  of  clover  is  unsatis- 
factory.    A  strip  across  the  field  should  be  dressed  with 
limestone  at  the  rate  of  forty  pounds  to  the  square  rod, 
and  its  effect  upon  the  growth  of  clover  noted. 

559.  Lime    Improves   the    Physical    Condition    of    Soil. 
Lime  also  has  a  very  marked  effect  on  the  physical  condition 
of  the  soil.     When  added  to  a  sandy  soil  it  tends  to  make 
the  soil  more  compact  by  partially  cementing  together  the 
particles  of  sand  and  thus  making  the  soil  capable  of  retain- 
ing larger  quantities  of  water.     When  used  on  clay  lands, 
on  the  other  hand,  lime  makes  the  soil  more  mellow.     A  clay 
soil  containing  very  little  lime  is  made  fine  with  the  greatest 
difficulty;    it  adheres  to  the  implements  used  when  wet, 
and  cracks  when  allowed  to  dry.     A  soil  rich  in  lime  crumbles 
more  easily  than  one  lacking  it,  is  readily  brought  into  good 
tilth,  and  does  not  adhere  to  any  appreciable  extent  to  the 
implements.     The  addition  of  lime  to  a  soil  containing  much 
clay  makes  the  soil  more  friable,  makes  it  possible  for  the 
rains  to  percolate  more  easily  through  the  soil,  and  over- 
comes the  danger  of  puddling.    The  puddling  of  clay  soils 


KEEPING  THE  SOIL  SWEET  481 

is  due  to  the  fact  that  the  clay  is  composed  of  very  small 
granules  which  fit  so  closely  together  that  the  water  cannot 
pass  between.  When  lime  is  added  to  the  soil  a  number 
of  these  small  particles  become  cemented  together  to  form 
a  much  larger  granule,  and  as  the  granules  increase  in  size 
the  spaces  between  them  also  become  larger. 

This  effect  of  lime  may  readily  be  shown  by  taking  a 
sample  of  clay,  adding  a  little  water,  working  it  thoroughly, 
and  then  allowing  it  to  dry.  As  a  result  of  this  treatment 
it  becomes  as  hard  as  a  brick.  If  to  another  portion  of  the 
clay  a  little  lime  is  added  (say  one  per  cent)  and  this  is  mois- 
tened, mixed  thoroughly,  and  allowed  to  dry,  it  will  be  found 
that  a  mere  touch  will  cause  it  to  crumble  to  pieces.  This 
granulated  condition  of  clay  soils,  so  easily  accomplished 
by  liming,  is  not  readily  destroyed  but  will  last  for  some 
years.  This  mechanical  effect  on  soils  is  more  marked 
in  the  case  of  quicklime  than  it  is  with  limestone. 

560.  Lime  Makes  Potential  Food  Available.  Lime  is 
useful  in  liberating  the  unavailable  food  materials  of  the 
soil.  Most  of  the  potassium  of  the  soil,  for  instance,  is 
locked  up  in  insoluble  silicates  and  is  not  available  to  plants. 
Lime  decomposes  some  of  these  silicates  and  converts  the 
potassium  into  forms  that  the  crop  can  use.  Experiments 
have  proved  that  when  lime  is  applied  to  a  soil  originally 
poor  in  this  substance,  the  plants  grown  are  not  only  richer 
in  lime  but  also  in  potash.  The  use  of  lime  then  may  for 
a  time  have  a  similar  effect  to  that  of  potash-containing 
manures,  but  it  must  be  remembered  that  the  lime  does  not 
supply  potash ;  it  merely  makes  available  the  potash  that  is 
present  in  the  soil;  and  if  the  store  of  potash  originally 
present  is  small,  it  will  probably  need  liberal  potash  manur- 
ing at  an  earlier  date  because  of  liming. 

EV.  CHEM.  —  31 


482  SOILS  AND  FERTILIZERS 

Lime  is  also  beneficial  in  preventing  the  formation  of  the 
very  insoluble  iron  and  aluminum  phosphates,  or  in  chang- 
ing them  to  calcium  phosphate  if  they  are  already  formed. 
Another  effect  of  adding  lime  or  limestone  to  an  acid  soil 
is  to  make  the  phosphates  of  the  soil  available. 

561.  Lime  not  a  Universal  Remedy.     So  much  has  been 
written  about  the  use  of  lime  that  there  is  danger  of  creat- 
ing the  impression  that  lime  or  limestone  is  the  universal 
remedy  for  all  unproductive  soils,  and  that  no  other  treat- 
ment than  liming  is  necessary.     It  must  be  remembered 
that  lime  adds  no  plant  food  save  calcium  to  the  soil,  but 
simply  brings  about  conditions  that  enable  the  crop  to  use 
larger  quantities  of  the  food  already  present,  so  that  if  used 
alone  it  makes  the  exhaustion  of  the  soil  more  rapid.    Lime 
can  in  no  way  take  the  place  of  good  tillage,  drainage,  manure, 
or  fertilizers.    There  is  an  old  saying  that  "  lime  makes  the 
father  rich,  but  the  son  poor,"  and  this  is  undoubtedly  true 
if  lime  is  used  alone.     It  has,  however,  a  legitimate  place 
in  agriculture,  and  if  used  in  connection  with  green  crops, 
barnyard  manure,  and  commercial  fertilizers  will  in  many 
cases  produce  beneficial  results. 

562.  Acid  Resistant  Plants.    Not  all  crops  are  seriously 
injured  by  an  acid  condition  of  the  soil.     Such  plants  as 
the  cranberry  and  blueberry  actually  require  an  acid  soil 
and  will  not  grow  on  one  that  is  alkaline.     Other  crops, 
while  not  preferring  an  acid  soil,  are  injured  but  little  by 
acidity.    The  potato  may  be  grown  very  successfully  on  an 
acid  soil  and  under  such  conditions  is  less  subject  to  the 
attacks  of  the  scab  fungus  than  when  grown  in  neutral  or 
alkaline  soils.     The  potato  scab  fungus  grows  more  readily 
in  an  alkaline  soil ;  consequently  lime  should  never  be  added 
to  the  soil  immediately  preceding  the  potato  crop. 


KEEPING  THE  SOIL  SWEET  483 


EXERCISES 

Ex.  343.  What  is  meant  by  a  sour  soil  ?  What  is  the  cause  /of 
acidity  in  soils?  What  effect  does  soil  acidity  have  on  plant  growth? 
What  plants  are  especially  sensitive  to  acidity?  What  effect  does 
acidity  have  on  the  fixation  of  nitrogen?  How  does  acidity  affect 
nitrification?  Why  is  limestone  necessary  for  nitrification? 

Ex.  344.  Explain  how  the  character  of  the  vegetation  indicates 
whether  or  not  soil  is  acid.  See  if  you  can  find  sorrel  growing  abundantly 
anywhere  in  the  vicinity  of  the  school.  What  should  you  suspect  re- 
garding the  soil  when  clover  fails  ? 

Ex.  345.  Test  a  number  of  soils  with  litmus  paper  (551).  Are  any 
of  the  soils  acid  ?  Mix  a  little  limestone  thoroughly  with  the  soil  and 
make  the  litmus  paper  test  again  on  the  following  day.  Give  the  result. 
Why  should  the  litmus  paper  never  be  handled  with  perspiring  fingers? 
Are  there  any  acid  soils  on  your  home  farm  ? 

Ex.  346.  Test  a  soil  for  acidity  by  the  Truog  test  as  follows: 
(1)  Prepare  the  lead  acetate  paper  by  dipping  a  piece  of  white  filter 
paper  into  a  10  per  cent  solution  of  lead  acetate.  Spread  the  paper 
on  a  pane  of  glass  to  dry.  (2)  Prepare  the  zinc  sulphide  and  calcium 
chloride  mixture  by  dissolving  50  grams  of  neutral  calcium  chloride 
in  250  cc.  of  water,  and  then  adding  5  grams  of  finely  pulverized  zinc 
sulphide.  (3)  To  perform  the  test  place  10  grams  of  soil  in  a  boiling 
flask,  adding  5  cc.  of  the  zinc  sulphide-calcium  chloride  mixture  and 
95  cc.  of  distilled  water.  Heat  to  boiling  and  boil  one  minute,  then 
place  a  strip  of  the  lead  acetate  paper  over  the  mouth  of  the  flask,  and 
boil  two  minutes.  A  darkening  of  the  acetate  paper  indicates  the 
presence  of  acid,  the  degree  of  acidity  being  approximately  shown  by 
the  depth  of  the  color.  What  causes  the  paper  to  darken?  Why  does 
it  not  change  color  if  the  soil  is  neutral  ?  Why  is  it  essential  that  the 
calcium  chloride  should  be  neutral  ? 

Ex.  347.  Test  some  soils  for  limestone  (553) .  Is  limestone  present  ? 
Is  this  test  of  general  application?  Would  there  be  any  need  of  liming 
a  soil  that  showed  the  presence  of  limestone  by  this  test? 

Ex.  348.  What  method  is  used  to  correct  the  acidity  of  soils? 
How  much  limestone  is  ordinarily  used  to  the  acre  ?  How  finely  should 
the  limestone  be  pulverized?  How  may  it  be  applied  to  the  soil? 


484  SOILS  AND  FERTILIZERS 

What  other  forms  of  lime  are  used  to  correct  acidity  ?  What  is  marl  ? 
Is  it  suitable  for  use  on  the  soil  ? 

Ex.  349.  What  is  the  principal  reason  for  using  limestone  ?  Why 
should  it  be  used  in  advance  of  clover  ?  Why  is  it  advisable  to  apply 
it  to  the  ground  that  has  been  plowed  for  corn?  How  should  you  con- 
duct a  field  test  with  limestone  ?  Is  such  a  test  advisable  ? 

Ex.  350.  Take  a  handful  of  wet  clay  and  thoroughly  knead  it 
into  a  ball  and  dry  it  in  the  oven.  Add  one  per  cent  of  lime  to  another 
handful  of  the  clay  and  knead  it  into  a  ball  and  dry  it  in  the  oven. 
How  do  the  two  samples  behave  when  broken  with  a  hammer  ?  What 
effect  does  lime  have  on  the  physical  condition  of  soils  ? 

Ex.  351.  Place  a  tablespoonful  of  clay  soil  in  each  of  two  tall 
glass  cylinders  or  bottles.  Shake  the  cylinders  to  get  the  clay  in  sus- 
pension. To  one  cylinder  add  a  little  slaked  lime  and  stir.  What 
difference  is  there  in  the  behavior  of  the  clay  in  the  two  cylinders? 
How  do  you  account  for  it  ?  Why  do  clays  puddle  ?  How  does  lime 
prevent  puddling  ? 

Ex.  352.  What  effect  does  lime  have  on  the  potential  plant  food 
of  the  soil  ?  Why  do  acid  soils  seem  to  contain  more  phosphorus  after 
liming  ?  In  what  form  is  the  phosphate  in  acid  soils  ?  If  a  farmer  uses 
lime  alone,  what  effect  will  it  eventually  have  on  the  fertility  of  his  land  ? 

Ex.  353.  Are  all  plants  injured  by  acidity?  Are  there  any  that 
prefer  an  acid  soil  ?  Why  should  care  be  used  in  liming  potato  soils  ? 


CHAPTER  LVI 
ORGANIC   MATTER 

563.  Old  and  New  Soils  Compared.     If  a  soil  that  has 
grown  crops  continuously  for  many  years  without  the  addi- 
tion of  plant  food  is  compared  with  an  adjacent  plot  of  virgin 
soil,  a  marked  difference  will  be  found  in  the  amounts  of 
organic  matter  that  the  two  soils  contain.     Soils  that  have 
been  under  cultivation  for  periods  of  twenty  to  thirty  years 
with  no  provision  for  maintaining  the  organic  matter  are 
found  to  contain  less  than  two  thirds  as  much  organic  matter 
as  the  original  soil.     There  can  be  no  doubt  that,  in  a  great 
many  instances,  the  loss  of  fertility  is  due  •  to  the  rapid 
decrease  in  the  amount  of  organic  matter. 

564.  Organic  matter  in  soils  is  largely  derived  from  the 
remains  of  the  plants  that  have  grown  on  them.     Under 
natural  conditions  the  entire  plant  becomes  a  part  of  the  soil 
and   furnishes   it   with   an   abundance   of  organic  matter. 
When  the  crop  is  removed  from  the  fiejd,  only  the  stubble 
and  roots  remain  to  supply  the  vegetable  matter,  but  the 
quantity  supplied  in  this  way  is  not  sufficient  for  the  best 
results.     Some  of  the  organic  matter  of  the  soil  is  of  animal 
origin,  but  the  amount  so  derived  is  insignificant  as  compared 
with  that  derived  from  vegetation. 

Organic  matter  exists  in  the  soil  in  all  stages  of  decomposi- 
tion.    Decay  begins  as  soon  as  the  plants  die  or  other  organic 

485 


486  SOILS  AND  FERTILIZERS 

matter  is  added  to  the  soil,  and  is  due  to  the  action  of  the 
bacteria  that  are  always  present  in  the  soil.  The  soil  con- 
tains, therefore,  fresh  vegetable  material  that  has  not  begun 
to  decay ;  partially  decayed  material  that  still  retains  a  part 
at  least  of  the  original  form ;  and  organic  matter  that  has 
so  completely  decomposed  that  it  has  entirely  lost  the  physi- 
cal structure  of  the  material  from  which  it  was  derived. 
The  black  waxy  material  coating  the  soil  grains,  giving  the 
dark  color  to  some  soils,  is  organic  matter  in  a  very  advanced 
state  of  decomposition,  and  is  known  as  humus.  The  term 
humus  is  often  used  as  a  synonym  of  the  term  organic 
matter.  Such  usage,  however,  is  incorrect,  as  much  more 
than  the  humus  is  included  in  organic  matter.  All  forms 
of  organic  matter  are  of  importance  in  the  soil ;  but  prob- 
ably that  part  which  is  undergoing  active  decay  is  the  most 
beneficial. 

565.  Organic  Matter  Increases  the  Amount  of  Soil 
Water.  Organic  matter  has  a  high  absorptive  power  for 
water.  A  sponge,  for  instance,  which  is  a  good  example 
of  organic  matter,  will  absorb  and  retain  more  than  ten 
times  its  own  weight  of  water.  Cellulose  and  other  forms 
of  vegetable  matter  will  hold  practically  the  same  amount 
of  water.  It  will  readily  be  seen,  therefore,  that  the  more 
organic  matter  the  soil  contains  the  greater  will  be  its  power 
to  store  water.  In  one  experiment  the  addition  of  one 
per  cent  of  organic  matter  to  the  soil  increased  its  water- 
holding  capacity  a  little  over  eight  per  cent.  The  water 
retained  by  the  organic  matter  is  in  large  part  so  loosely 
held  that  it  can  be  utilized  by  growing  plants.  The  follow- 
ing table  gives  the  amount  of  water  held  in  a  cubic  foot 
of  three  different  soils  with  varying  amounts  of  organic 
matter : 


ORGANIC  MATTER  487 


KIND  OF  SOIL 

POUNDS  OF  WATER  IN 
ONE  CUBIC  FOOT 

Sand                                      

27.3 

Sandy  loam                                    

38.8 

Loam      

41.4 

It  will  be  seen  that  the  quantity  of  water  increases  with 
the  amount  of  organic  matter  present,  the  sand  containing 
the  least,  and  the  loam,  which  has  the  largest  percentage  of 
organic  matter,  containing  much  inore.  It  is  evident  from 
the  above  that  one  of  the  best  ways  to  enable  the  soil  to 
store  water  from  the  spring  rains  for  the  use  of  the  growing 
crop  during  the  hot  summer  months  is  to  keep  the  soil  well 
supplied  with  organic  matter. 

566.  Organic    Matter    a    Storehouse    for    Plant    Food. 
The  organic  matter  of  the  soil  contains  part  of  the  plant 
food  that  was  utilized  by  plants  formerly  grown  on  the 
soil.     It  has  been  shown  that  most  of  the  nitrogen  in  the 
soil  is  present  in  the  organic  matter  and  that  this  becomes 
available  through  the  gradual  decay  of  the  plant.     It  is  fortu- 
nate that  most  of  the  nitrogen  is  stored  in  organic  matter ; 
for  if  it  were  all  immediately  converted  into  nitrates,  there 
would  be  great  loss  by  leaching,  since  the  nitrates  are  very 
soluble  and  the  soil  has  little  power  of  retaining  them. 

567.  Organic  Matter  Makes  Potential  Food  Available. 
The  presence  of  decomposing  organic  matter  in  the  soil  is 
an  important  factor  in  making  the  mineral  elements  of  plant 
food  available.     During  decay  certain  acids,  such  as  lactic, 
acetic,  and  nitrous  acids,  are  produced,  and  these  undoubtedly 
have  a  solvent  action  on  the  mineral  matters  of  the  soil, 
tending  to  make  them  more  available  to  the  plant.     Perhaps 


488  SOILS  AND  FERTILIZERS 

quite  as  important  a  factor  is  the  large  amount  of  carbonic 
acid  formed  during  the  prpcess  of  decay.  This  carbonic 
acid  dissolved  in  the  soil  water  is  of  prime  importance  in 
the  production  of  soluble  plant  food,  and  it  also  has  a  bene- 
ficial effect  on  the  physical  condition  of  the  soil,  especially 
if  the  soil  contains  a  large  amount  of  clay. 

568.  Organic   Matter  Improves   Soil  Texture.     Organic 
matter  is  also  valuable  in  improving  the  physical  condition 
of  the  soil.     Sandy  soils  are  made  more  compact  by  its 
presence  and  better  able  to  supply  a  crop  with  food  and 
moisture.     Clay  soils,  on  the  other  hand,  are  made  more 
mellow  by  the  addition  of  organic  matter.     Clay  is  likely 
to  become  too  compact  unless  there  is  a  certain  amount  of 
organic  matter  present  to  prevent  it.     The  better  tilth  of  a 
soil  due  to  the  presence  of  organic  matter  facilitates  drain- 
age and  ventilation,  both  of  which  are  necessary  to  the  pro- 
motion of  soil  sanitation. 

Organic  matter  is  an  essential  part  of  all  true  soils.  In 
most  soils  there  is  a  marked  difference  in  color  and  texture 
between  the  surface,  or  true,  soil  and  the  subsoil.  The  sur- 
face soil  is  darker  in  color,  less  compact,  and  more  easily 
worked  by  tillage  implements  than  is  the  subsoil.  The 
difference  is  due  largely  to  the  greater  amount  of  organic 
matter  contained  in  the  surface  soil.  The  darker  color  of 
the  soil  is  due  largely  to  humus,  the  very  black  soils  con- 
taining large  quantities  of  humus.  Organic  matter,  more 
especially  humus,  also  affects  the  temperature  of  the  soil,  for 
the  darker-colored  soils  absorb  more  heat  from  the  sun's 
rays  than  do  the  lighter-colored  ones. 

569.  Loss  of  Organic  Matter.     Investigations  have  shown 
conclusively  that  as  the  organic  content  of  the  soil  is  de- 
creased by  constant  cultivation  and  cropping,  the  nitrogen 


ORGANIC  MATTER 


489 


content  of  the  soil,  the  amount  of  moisture  that  it  contains, 
and  the  crop  production  are  likewise  decreased. 

All  the  methods  so  far  discussed  for  making  potential 
plant  food  available  tend  to  decrease  the  amount  of  organic 
matter  in  the  soil.  Tillage,  drainage,  bare  fallowing,  and 
liming  the  soil  all  increase  the  amount  of  food  available  to 
the  crop,  because  they  present  ideal  conditions  for  the  de- 
composition of  organic  matter  in  the  soil ;  but  dependence 
upon  these  methods  alone  will  eventually  result  in  injury 
through  loss  of  organic  matter.  The  loss  of  nitrogen  and 
organic  matter  is  strikingly  shown  in  the  following  table : 


NATIVE  SOIL 
PER  CENT 

CULTIVATED  23 
YEARS 
PER  CENT 

Loss 
PER  CENT 

Organic  matter    .... 

3.97 

2.59 

1.38 

Nitrogen     

0.36 

0.19 

0.17 

Capacity  to  hold  water 

62.00 

54.00 

8.00 

The  foregoing  statements  should  not  be  construed  as  argu- 
ments against  tillage,  drainage,  and  liming,  because  the  de- 
struction of  organic  matter  is  an  essential  part  of  good  farm- 
ing. It  is  the  farmer's  business  to  bring  about  in  the  soil 
the  proper  conditions  for  the  rapid  decay  of  organic  matter 
so  that  the  crops  may  utilize  the  plant  food  therein  contained. 
However,  if  he  is  to  have  continued  success  in  producing 
crops,  the  farmer  must  at  the  same  time  return  organic 
matter  to  replace  that  which  has  been  destroyed. 

670.  Restoring  Organic  Matter.  Under  farm  conditions 
where  most  of  the  crops  must  be  removed  from  the  field, 
the  maintenance  of  the  supply  of  organic  matter  is  a  serious 
problem.  A  certain  amount  of  organic  matter  is  left  behind 
in  the  stubble  and  the  roots.  This  material  should  be  utilized 


490  SOILS  AND  FERTILIZERS 

to  the  fullest  extent.  The  practice  of  burning  over  the 
field  to  destroy  the  stubble  before  plowing  is  to  be  condemned, 
because  large  quantities  of  organic  matter  are  destroyed  in 
this  way.  The  straw,  cornstalks,  and  any  similar  material, 
if  not  used  for  feeding,  should  be  incorporated  into  the  soil. 
The  burning  of  any  of  the  organic  matter  of  the  farm  or 
garden  is  never  justified  except  when  necessary  to  prevent 
the  spread  of  plant  diseases. 

Large  amounts  of  organic  matter  may  be  restored  to  the 
soil  by  a  careful  use  of  the  stable  manure.  The  manure 
from  the  domestic  animals  contains  nearly  one  half  of  the 
organic  matter  of  the  feeds,  the  rest  having  been  oxidized 
in  the  animal  body  and  given  off  largely  as  carbon  dioxide 
and  water.  If  the  manure  is  properly  handled,  therefore, 
about  one  half  of  the  organic  matter  in  all  feeds  used  may 
be  added  to  the  soil.  The  precautions  necessary  to  obtain 
these  results  are  discussed  in  Chapter  LVIII. 

The  plowing  under  of  grass  sods  adds  organic  matter  to 
the  soil.  Such  grasses  as  Kentucky  blue  grass,  especially, 
fill  the  soil  full  of  small,  fibrous  roots  and  when  the  sod  is 
plowed  the  roots  and  the  stubble  begin  to  decay.  In  one 
instance  the  first  six  inches  of  soil  in  a  field  of  timothy  and 
redtop  were  found  to  contain  nearly  four  tons  of  roots  and 
stubble  to  the  acre.  Pasture  lands,  if  well  fertilized  so  as 
to  grow  an  abundance  of  grass,  may  be  used  as  a  means  of 
maintaining  the  organic  matter  of  the  farm. 

571.  Green  Manuring.  On  many  farms  even  the  com- 
plete utilization  of  the  various  methods  outlined  in  the  last 
section  will  not  suffice  to  maintain  the  necessary  amount  of 
organic  matter  in  the  soil  for  the  production  of  maximum 
crops.  Under  such  conditions  it  is  necessary  to  grow  a 
crop  for  the  express  purpose  of  plowing  it  under  to  increase 


ORGANIC  MATTER 


491 


FIG.  229.  —  Plowing  under  a  green  manure 
crop. 


the  organic  matter  of  the  soil.  Such  a  practice  is  known  as 
green  manuring.  Plowing  under  green  crops  raised  for 
that  purpose  is  one  of  the  oldest  means  of  improving  the 
fertility  of  the  soil.  It  was  advocated  by  Roman  writers 
more  than  two  thousand  years  ago,  and  has  been  in  more 
or  less  common  use  among  progressive  farmers  ever  since. 

The  value  of  green 
manuring  depends  pri- 
marily on  the  fact  that 
it  increases  the  amount 
of  organic  matter  in  the 
soil.  Several  kinds  of 
crops  may  be  used  as 
green  manures,  but  the 
most  valuable  for  this 
purpose  are  the  legumes. 
The  discovery  that  the  leguminous  plants  can,  through 
the  nodule-forming  bacteria,  fix  the  free  nitrogen  of  the  air, 
has  thrown  a  new  light  on  green  manuring  and  the  plants 
adapted  to  this  purpose.  The  legumes  have  all  the  advan- 
tages of  the  other  plants  in  providing  organic  matter,  and  at 
the  same  time  they  increase  the  amount  of  nitrogen  in  the  soil. 
They  are,  as  a  rule,  deeper-rooted  plants  and  are  supposed 
to  bring  up  mineral  food  from  the  subsoil,  and  leave  it  where 
it  will  be  within  reach  of  the  more  shallow-rooted  plants. 
Of  the  legumes  the  crops  most  often  recommended  are  red 
clover,  sweet  clover,  cowpea,  crimson  clover,  the  lupines, 
soy  bean,  and  the  ordinary  field  bean,  and  field  pea.  Of 
these,  red  clover  is  probably  the  one  most  generally  used. 

572.  Green  Manuring  and  Type  of  Farming.  Such  crops 
as  red  clover,  which  make  the  best  green  manures,  also  have 
great  value  as  feeds  for  live  stock,  and  it  may  be  found  more 


492 


SOILS  AND  FERTILIZERS 


profitable  to  feed  them  to  animals  and  return  the  manure 
to  the  soil  than  it  is  to  turn  them  under.  But  even  on  stock 
farms  it  is  often  advisable  to  plow  under  the  second  growth 
of  clover  instead  of  cutting  it  for  hay. 

In  any  system  of  farming  in  which  the  crops  are  sold  from 
the  farm,  some  provision  for  green  crops  to  plow  under  is 
absolutely  necessary,  and  the  rotation  used  should  include 
a  green  manure  crop.  The  increase  in  the  other  crops  from 
this  practice  will  more  than  make  up  for  the  fact  that  there 
is  no  crop  to  sell  from  the  green  manure  field. 

573.  Catch  Crops  for  Green  Manuring.  Where  it  is  in- 
advisable to  devote  an  entire  season  to  the  growth  of  a 
crop  for  green  manuring,  good  results  may  often  be  ob- 
tained by  the  use  of 
what  is  known  as  a 
catch  crop,  or  a  crop 
grown  between  two 
main  crops.  Rye  is 
often  planted  in  the 
corn  land  at  the  time 
of  the  last  cultivation 
and  allowed  to  grow 
until  the  ground  is 
plowed  the  following 
spring,  thus  adding  or- 
ganic matter  to  the 
soil.  In  the  southern  states  crimson  clover  and  other  leg- 
umes are  used  in  a  like  manner,  but  in  the  north  the  legumes 
are  uncertain  as  catch  crops.  A  mixture  of  rye  and  hairy 
vetch  is  very  satisfactory  as  a  catch  crop  after  corn.  The 
use  of  cover  crops  in  orchards  is  another  example  of  a 
catch  crop. 


FIG.  230.  —  Crimson  clover  as  an  orchard 
cover  crop. 


ORGANIC  MATTER  493 

574.  Danger  from  Green  Manuring.  While  green  manur- 
ing is  a  valuable  method  of  increasing  the  humus  supply 
of  the  soil,  it  is  not  unattended  by  danger.  In  a  dry  season, 
for  instance,  the  growth  of  a  crop  to  plow  under  may  result 
in  lowering  the  moisture  content  of  the  soil  to  a  point  that 
is  detrimental  to  the  succeeding  crop.  There  is  also  danger 
in  such  a  season  that  there  may  not  be  sufficient  moisture 
in  the  soil  to  bring  about  the  decomposition  of  the  organic 
matter  that  is  turned  under,  the  result  being  serious  injury 
to  the  physical  condition  of  the  soil.  Such  injury,  however, 
does  not  frequently  occur,  and  its  bad  effects  are  only  tem- 
porary. If  a  crop  is  plowed  under  during  a  dry  season,  the 
ground  should  be  rolled  with  a  heavy  roller  so  as  to  renew 
the  capillary  movement  of  moisture  between  the  surface 
and  the  subsoil. 

EXERCISES 

Ex.  354.  If  possible,  obtain  a  sample  of  soil  from  the  center  of  a 
field  that  has  been  under  cultivation  for  a  long  time,  and  another 
sample  from  the  fence  row  of  the  same  field.  What  difference  do  you 
note  in  the  two  samples?  Does  the  soil  from  the  fence  row  contain 
more  organic  matter  than  the  other  ?  What  is  the  source  of  the  organic 
matter  in  soils?  What  is  meant  by  humus?  Is  humus  identical  with 
organic  matter?  What  gives  the  black  color  to  some  soils? 

Ex.  355.  Weigh  a  large  sponge  after  it  has  been  thoroughly  dried. 
Now  dip  the  sponge  in  water,  hold  it  up  until  dripping  has  ceased, 
and  weigh  it  again.  How  many  times  its  own  weight  of  water  will  the 
sponge  hold?  What  can  you  say  about  the  power  of  organic  matter 
to  increase  the  water-holding  capacity  of  the  soil  ? 

Ex.  356.  Determine  the  water-holding  capacity  of  a  soil  as  de- 
scribed in  Ex.  318.  Add  to  another  sample  of  the  soil  one  per  cent  of 
ground  moss  or  wheat  bran  and  determine  the  water-holding  capacity. 
How  much  does  the  organic  matter  increase  the  water  in  the  soil  ? 

Ex.  357.  Explain  what  is  meant  by  the  statement  that  organic 
matter  is  a  storehouse  of  plant  food.  How  is  this  plant  food  made 


494  SOILS  AND  FERTILIZERS 

available?  How  does  organic  matter  make  the  mineral  food  of  the 
soil  available  ? 

Ex.  358.  Note  the  difference  in  appearance  between  the  surface 
soil  and  the  subsoil.  What  makes  the  surface  soil  darker  in  color  and 
more  friable  than  the  subsoil  ?  What  effect  does  organic  matter  have 
on  the  texture  of  a  sandy  soil  ?  Of  a  clay  soil  ? 

Ex.  359.  Explain  how  organic  matter  is  lost  from  the  soil.  Show 
how  some  of  it  may  be  restored  by  the  plant  residues,  by  the  use  of 
stable  manure,  and  by  plowing  under  sods. 

Ex.  360.  What  is  meant  by  green  manuring?  Is  it  a  modern 
practice  ?  What  advantages  have  the  legumes  as  green  manure  crops  ? 
What  are  the  crops  most  commonly  used  as  green  manures?  In  what 
type  of  farming  is  green  manuring  desirable  ? 

Ex.  361.  What  are  catch  crops  and  how  may  they  be  used  to 
increase  the  organic  matter  of  the  soil?  Give  an  example  of  the  use 
of  catch  crops.  Are  there  any  dangers  connected  with  green  manur- 
ing? Why  should  the  roller  be  used  when  a  heavy  crop  is  plowed 
under? 


CHAPTER  LVII 
ROTATION   OF   CROPS 

575.  Origin  of  Rotations.     It  is  the  common  knowledge 
of  farmers  in  those  parts  of  the  world  where  the  land  has 
been  cultivated  for  a  long  time  that  the  fertility  of  the 
soil  is  maintained  for  a  much  longer  time  by  growing  a  variety 
of  crops  than  by  producing  one  crop  continuously.     The 
adoption  of  a  system  of  rotation  of  crops  has  been  the  out- 
growth of  accident  rather  than  the  result  of  an  understand- 
ing of  its  underlying  principles.     The  system  of  alternating 
years  of  bare-fallow  and  wheat  may  be  said  to  be  a  two-year 
rotation  and  was  the  first  to  be  adopted.     History  teaches 
us  that  this  was  later  followed  by  a  three-year  rotation  con- 
sisting of  fallow,  wheat,  beans,  or  oats ;  and  still  later,  when 
the  value  of  clover  and  fallow  crops  became  evident,  this 
rotation  gave  way  to  the  now  famous  Norfolk  rotation  of 
turnips,    barley,    clover,    and   wheat,    the   typical   English 
rotation.     The    Norfolk    four-year    course    represents    the 
more  common  type  the  world  over,  consisting  as  it  does  of 
cereals  alternating  with  hoed  crops  and  leguminous  crops. 

576.  Plants   Differ  in  Food   Requirements.     There  are 
many  arguments  to  be  advanced  in  favor*  of  growing  a  variety 
of  crops  on  the  soil.     The  different  crops  vary  in  their  food 
requirements  and  in  their  ability  to  procure  this  food  from 
the  soil.     When  one  crop  is  grown  continuously  on  the  same 
field,  nearly  all  the  plant  food  that  it  finds  available  may 
become  exhausted,  although  the  soil  will  still  contain  large 
quantities  of  food  in  forms  that  could  be  assimilated  by  plants 

495 


496  SOILS  AND  FERTILIZERS 

of  another  class.  Some  crops  evidently  require  the  mineral 
matter  to  be  in  a  readily  soluble  form,  while  others  can  use 
less  available  forms  of  plant  food.  Other  crops  make  an 
especial  drain  on  one  element  of  plant  food.  By  growing 
plants  with  different  food  requirements  the  different  ele- 
ments are  more  evenly  used,  and  there  is  less  likelihood 
of  any  one  element  becoming  exhausted. 

577.  Plants  Differ  in  Manner  of  Growth.     The    various 
crops  differ  widely  in  their  systems  of  root  growth.     Some 
plants,  as  wheat,  for  example,  are  comparatively  shallow- 
rooted  and  must  obtain  their  food  from  the  surface  soil. 
Others,  as  the  clovers,  are  very  deep-rooted  and  are  able 
to  use  food  that  is  not  within  the  reach  of  the  more  shallow- 
rooted  plants.     The  deep-rooted  plants  are  not  only  able 
to  procure  the  low-lying  food,  but  probably  bring  a  part 
of  it  to  the  surface,  where  it  remains,  upon  their  decay,  for 
the  use  of  the  succeeding  crop.     It  is  well  known  that  the 
shallow-rooted  plants  do  better  when  preceded  by  a  deep- 
rooted  crop. 

578.  Rotation  Improves  the  Soil  and  Economizes  Labor. 
When  plants  of  different  varieties  are  grown,  the  soil  receives 
different  treatment  for  each  crop ;   so  that  the  faults  of  one 
year  are  likely  to  be  corrected  the  next  year.     Thereby  the 
soil  is  kept  in  much  better  physical  condition.     As  a  general 
rule  the  ground  can  be  better  prepared  for  the  succeeding 
crop  if  a  judicious  rotation  is  practiced  than  if  the  same  crop 
is  grown  continuously.     The  roots  and  stubble  of  clover 
and  grasses  are  also  factors  of  some  importance  in  improv- 
ing the  texture  of  the  soil.    Everything  considered,  the  tilth 
of  the  soil  will  be  found  to  be  much  improved  by  rotation. 

The  growing  of  a  variety  of  crops  on  the  farm  results 
in  economy  of  labor ;  for  the  work  of  caring  for  them  is  dis- 


ROTATION  OF  CROPS  497 

tributed  throughout  the  season  instead  of  all  coming  at  one 
time.  In  this  way  it  is  possible  to  secure  cheaper  and  better 
help  than  when  only  a  few  kinds  of  plants  are  raised. 

579.  Rotation  Aids  in  Controlling  Diseases,  Insects, 
and  Weeds.  Rotation  also  enables  the  farmer  to  control 
plant  diseases  and  to  head  off  the  injurious  insects.  Most 
of  the  plant  diseases  are  caused  by  bacteria  or  fungi  that 
live  only  on  one  genus  of  plants,  or,  at  any  rate,  are  more  or 
less  restricted  in  the  number  of  crops  that  they  can  use  as 
host  plants.  Where  one  crop  is  grown  continuously,  these 
disease-producing  fungi  have  every  opportunity  to  be  car- 
ried over  from  one  year  to  another.  Most  of  the  injurious 
organisms  are  comparatively  short-lived,  so  that  if  three 
or  four  years  of  crops  that  are  not  suitable  host  plants  inter- 
vene, these  organisms  are  likely  to  be  destroyed. 

In  the  same  way  it  may  be  said  that  the  injurious  insects 
are  limited  to  certain  plants  for  their  food  supply,  and  if 
these  plants  are  not  grown  on  the  field  for  a  number  of  years, 
the  insects  may  die  from  starvation.  These  remarks  do 
not  apply,  of  course,  to  those  insects  that  have  migratory 
powers.  There  is  no  doubt  that  both  diseases  and  insects 
can  be  more  easily  suppressed  if  rotation  is  practiced. 

Where  one  crop  is  grown  continuously,  the  soil  becomes 
infested  with  certain  weeds  that  are  not  destroyed  by  the 
system  of  tillage  necessary  for  that  crop.  The  varying 
treatment  to  which  a  soil  is  subjected  in  a  well-planned  rota- 
tion makes  this  condition  impossible ;  so  that  the  destruction 
of  weeds  may  be  considered  as  one  of  the  very  desirable 
results  of  a  rotation  of  crops.  In  lands  badly  infested  with 
particular  weeds  it  may  even  be  desirable  to  omit  from  the 
rotation  for  a  while  the  crop  whose  growth  presents  the  best 
condition  for  the  propagation  of  these  weeds. 

BV.    CHEM. 32 


498 


SOILS  AND  FERTILIZERS 


CONTINUOUS  CROPPING' 

IZTPfRIOD   2QPERIOD  3? PERIOD 
25.258U.    I&75  BU.    /0.43 8U 


FIVE-YEAR  ROTATION 

1 5J PERIOD  ^  9 PERIOD  39 PERIOD 
3/ 89  BU.   30.82  BU  3I.O4 BU. 


FlG.  231.  —  Showing  the  advantage  of  rotation  in  corn  production. 

580.  Rotation  Increases  Crop  Yields.  When  crops  are 
grown  in  rotation,  each  crop  gives  a  higher  yield  than  when 
it  is  grown  continuously  on  the  same  field.  This  is  true 
whether  the  crops  are  grown  with  or  without  manures  or 
fertilizers.  The  effect  of  rotation  upon  the  yield  is  shown 
in  the  following  table,  which  gives  the  average  yield  for  the 
third  five-year  period  of  three  different  crops  grown  con- 
tinuously, and  in  a  five-year  rotation  at  the  Ohio  Experi- 
ment Station. 


CROP 

UNFERTILIZED 

STABLE 
MANURE 

COMMERCIAL 
FERTILIZERS 

Corn 
Grown  continuously      .     . 
Grown  in  rotation  .     .     . 

10  bu. 
31  bu. 

24  bu. 
50  bu. 

39  bu. 
54  bu. 

Oats 
Grown  continuously     .     ,  • 
Grown  in  rotation    .     .     . 

22  bu. 
33  bu. 

35  bu. 
42  bu. 

45  bu. 
53  bu. 

Wheat 
Grown  continuously      .     .; 
Grown  in  rotation    . 

6bu. 
14  bu. 

12  bu. 
25  bu. 

17  bu. 
33  bu. 

ROTATION   OF  CROPS  499 

581.  Planning  a  Rotation.     In  planning  a  rotation  the 
farmer  must  be  guided  by  his  own  conditions  and  his  re- 
quirements in  the  way  of  crops.     A  rotation  for  a  dairy 
farm,  for  example,  might  be  quite  different  from  one  for  a 
farm  devoted  to  the  production  of  grain  for  the  market. 
A  few  general  rules,  however,  will  apply  to  all  rotations. 
Every  rotation  should  include  one  intertilled  or  hoed  crop, 
such  as  corn,  potatoes,  or  cotton,  in  order  that  the  soil  may 
receive  the  benefit  of  such  a  crop  in  the  way  of  destroying 
weeds,  improving  the  tilth,  and  setting  free  potential  plant 
food.     At  least  one  leguminous  crop  should  be  included. 
A  crop  that  is  exacting  in  its  food  requirements  should  be 
followed  by  one  less  exacting.     In  general  terms,  the  crops 
should  vary  as  much  as  possible  in  their  food  requirements, 
manner  of  growth,  root  systems,  and  the  season  of  the  year 
in  which  they  occupy  the  ground.     Whenever  possible,  the 
rotation  should  include  a  catch  crop  or  provide  some  other 
method  of  insuring  an  adequate  supply  of  organic  matter. 
Fertilizers  should  be  applied  to  the  particular  crop  or  crops 
that  will  give  the  most  profitable  returns  for  their  use. 

582.  Some  Typical  Rotations.     Rotations  are  in  use  that 
cover  periods  varying  from  two  to  seventeen  years.     In 
general,  short  rotations  of  three  to  five  years  are  more  in 
favor  than  very  long  ones.     A  few  examples  will  exemplify 
the  principles  of  rotation. 

A  common  five-year  rotation  is  as  follows:  Corn,  oats, 
wheat,  clover,  and  timothy,  each  one  year.  Rye  may  be 
seeded  as  a  catch  crop  in  the  corn. 

Corn,  wheat,  and  clover  form  a  common  three-year  rota- 
tion, the  ground  being  plowed  for  the  corn,  and  the  wheat 
seeded  in  the  corn  stubble  after  disking. 

Potatoes,  wheat,  and  clover  are  popular  as  a  rotation 


500  SOILS    AND    FERTILIZERS 

in  some  of  the  good  potato  sections.  The  clover  is  plowed 
under  for  potatoes  and  a  heavy  application  of  fertilizers 
is  used. 

A  rotation  often  used  on  dairy  farms  consists  of  corn, 
oats,  and  clover,  besides  timothy  for  pasture.  A  catch 
crop  may  be  used  in  the  corn. 

A  rotation  that  has  been  recommended  for  grain  farming 
in  the  Middle  West  is  corn,  oats,  clover,  and  wheat.  The 
clover  is  plowed  for  wheat  and  all  the  straw  and  cornstalks 
are  plowed  under.  A  catch  crop  of  clover  is  also  grown 
between  the  wheat  and  corn.  Ground  rock  phosphate 
(609)  is  plowed  under  with  the  clover. 

A  rotation  advocated  for  the  cotton-growing  sections 
consists  of  cotton,  corn,  oats,  and  cowpeas,  the  last  named 
crop  being  plowed  under  as  a  green  manure. 

Over  forty  different  rotations  are  in  use  in  one  state, 
many  of  which,  however,  do  not  meet  the  requirements  sug- 
gested above  for  planning  the  rotation. 

EXERCISES 

Ex.  362.  Explain  the  evolution  of  the  rotation  of  crops.  Is 
rotation  of  crops  desirable?  Outline  the  reasons  in  favor  of  rotation 
under  these  headings  :  (1)  Food  requirements  of  plants.  (2)  Manner 
of  growth.  (3)  Effect  upon  soil  and  economy  of  labor.  (4)  Effect 
upon  diseases,  insects,  and  weeds. 

Ex.  363.  Are  the  yields  of  the  various  crops  increased  by  rotat- 
ing? Give  the  general  rules  for  planning  a  rotation.  What  rota- 
tion is  used  on  your  home  farm?  Do  you  use  catch  crops?  Do  you 
grow  any  crop  to  plow  under  ?  How  many  different  rotations  can  you 
find  in  use  in  your  community  ?  How  do  they  accord  with  the  sugges- 
tions for  planning  a  rotation? 


CHAPTER  LVIII 
STABLE    MANURE 

583.  IF  the  crop  yields  are  not  to  decrease,  some  way 
must  be  provided  to  replace  in  the  soil  the  plant  food  re- 
moved by  the  crops.     This  is  done  by  the  use  of  stable 
manure  and  commercial  fertilizers. 

584.  Importance  of  Stable  Manure.     Stable  manure  is 
the  oldest  and  is  still  the  most  used  of  all  fertilizers.     It  has 
stood  the  test  of  long  experience,  and  has  proved  its  posi- 
tion as  one  of  the  most  important  manures.     The  fact  that 
the  application  of  the  excrement  of  animals  to  the  soil 
results  in  increased  crop  production   is  mentioned  by  the 
early  Roman  writers,  and  from  that  time  to  the  present 
the  majority  of  farmers  have  placed  their  main  reliance  on 
this  class  of  manures  for  maintaining  fertility  of  the  land. 

The  importance  of  manure  is  shown  by  the  fact  that  the 
quantity  produced  annually  by  the  domestic  animals  of  the 
United  States  contains  an  amount  of  nitrogen,  phosphorus, 
and  potassium  that  would  cost  $2,458,470,000  if  pur- 
chased in  the  cheapest  forms  of  commercial  fertilizers. 
More  than  one  third  of  the  value  of  the  manure  is  lost 
through  improper  handling,  and  this  loss  is  replaced  only 
in  small  part  by  the  one  hundred  million  dollars'  worth  of 
commercial  fertilizers  purchased  annually  by  the  farmers 
of  this  country.  This  loss  of  plant  food  is  the  more  unfor- 
tunate because  it  could  in  great  measure  be  prevented. 

585.  Valuation  of  Manure  and  Fertilizers.     Since  some 
way  of  stating  the  value  of  manure  is  desirable,  it  is  custom- 

501 


502  SOILS   AND  FERTILIZERS 

ary  to  use  the  same  method  that  is  employed  in  calculating  the 
value  of  commercial  fertilizers ;  namely,  to  base  the  valua- 
tion on  the  quantities  of  nitrogen,  phosphorus,  and  potas- 
sium that  the  manure  or  fertilizer  contains,  ignoring  any 
other  constituents  that  may  be  present.  The  fertilizer 
trade  has  always  stated  phosphorus  not  as  the  element  but 
as  the  anhydride,  P2O5,  which  is  termed  phosphoric  acid  in 
the  trade  (179).  Likewise  potassium  is  stated  as  the  oxide, 
K2O,  under  the  trade  name  of  potash.  One  pound  of  phos- 
phorus is  equivalent  to  2.3  pounds  of  phosphoric  acid 
(P2O8).  One  pound  of  potassium  is  equivalent  to  1.2  pounds 
of  potash  (K2O) .  Nitrogen  is  sometimes  stated  as  ammonia 
(NH3) ,  but  this  term  is  not  so  commonly  used  as  are  the  terms 
phosphoric  acid  and  potash.  One  pound  of  nitrogen  is  the 
equivalent  of  1.2  pounds  of  ammonia.  As  these  names  are 
used  almost  exclusively  in  the  fertilizer  trade,  and  most 
commonly  in  the  writings  on  manures  and  fertilizers,  and 
are  also  recognized  by  law  in  nearly  all  the  states,  it  seems 
best  to  employ  them  in  this  text.  The  term  phosphoric  acid 
as  used  in  discussing  fertilizers  does  not  mean  true  phos- 
phoric acid  (H3PO4)  (175)  nor  does  the  potash  of  the  fer- 
tilizer trade  mean  true  potash  (K2CO3)  (204). 

For  purposes  of  valuation  nitrogen  is  given  a  price  of  15 
cents  a  pound,  and  phosphoric  acid  and  potash  are  quoted  at 
5  cents  a  pound  each.  These  are  average  prices  for  the  past 
decade  and  will  be  used  in  all  the  calculations  in  this  text. 

586.  Composition  of  Manure  from  Different  Animals. 
The  manures  produced  by  the  various  classes  of  animals 
differ  in  their  composition  and  in  their  physical  properties. 
The  following  table  gives  the  amount  and  value  of  the 
plant  food  in  one  ton  of  manure  of  the  common  domestic 
animals. 


STABLE  MANURE 


503 


ANIMAL 

NITROGEN 

PHOSPHORIC 
ACID 
P2O6 

POTASH 
K20 

VALUE  PER 
TON 

Cow    

91b. 

3  Ib. 

8  Ib 

$1  89 

Pig 

9  Ib. 

4lb. 

12  Ib 

2  14 

Horse       .     .     .     .     .     . 

12  Ib. 

61b. 

11  Ib 

255 

Sheep       ....    .     . 

17  Ib. 

51b 

13  Ib 

3  39 

Chicken        ... 

28  Ib 

18  Ib 

7  Ib 

544 

The  difference  in  the  value  per  ton  of  the  manures  is 
largely  due  to  the  varying  amounts  of  water  which  they 
contain.  Chicken  manure,  sheep  manure,  and  horse  manure 
contain  less  water  than  the  manure  from  pigs  and  cows. 

While  the  table  shows  that  there  is  a  decided  difference 
in  the  value  of  a  ton  of  the  different  manures,  it  is  also  true 
that  the  value  of  the  total  amount  of  manure  produced  from 
the  same  feeding  stuffs  does  not  vary  much  for  the  different 
animals.  If  the  same  kinds  and  amounts  of  feeds  were 
given  to  cows  and  to  sheep,  for  instance,  the  cows  would 
produce  more  tons  of  a  wetter  manure  than  the  sheep ;  but 
the  total  value  would  be  about  the  same  in  either  case. 

587.  Factors    Affecting    the    Value    of    Fresh    Manure. 
The  value  of  stable  manure  as  produced,  and  before  it  has 
been  subjected  to  any  of  the  losses  to  be  discussed  later,  is 
largely  determined  by  five  principal  factors:    namely,  (1) 
the  kind  of  feeds,  (2)  the  age  of  the  animal,  (3)  the  kind  of 
animal,  (4)  the  products  from  the  animal,  (5)  the  kind  and 
amount  of  litter  used. 

588.  Kind  of  Feeds.    The  total  value  of  the  manure 
produced  by  a  given  live  weight  of  animals  depends  upon 
the  quality  and  the  quantity  of  the  feeding  stuffs  used  in 
the  ration.     Feeds  vary  greatly  in  the  amount  of  plant  food 


504  SOILS  AND  FERTILIZERS 

that  they  contain.  The  fertilizing  value  of  a  ton  of  timothy 
hay,  for  example,  is  $5.21 ;  of  clover  hay,  $8.79 ;  of  wheat 
bran,  $12.52 ;  and  of  cottonseed  meal,  $23.20.  Animals 
fed  on  food  substances  low  in  fertilizing  value  will  produce 
manure  of  a  correspondingly  low  value.  In  one  experiment 
with  two  lots  of  pigs,  one  of  which  was  fed  on  corn  meal  and 
bran,  and  the  other  on  corn  meal  and  meat  scraps,  the 
manure  produced  by  the  latter  had  twice  the  value  of  that 
from  the  pigs  fed  corn  and  bran. 

589.  Age  of  the  Animal.    Young  animals  use  some  of 
the  nitrogen  compounds  of  the  ration  to  build  their  muscles, 
and  a  part  of  the  phosphoric  acid  and  calcium  is  utilized  in 
forming  bone.    Mature  animals,  whose  bones  and  muscles 
are  already  developed,  retain  in  their  bodies  very  little  of 
the  fertilizing  constituents  of  the  feeds.     Manure  from  young 
and  growing  animals,  therefore,  has  a  lower  value  than  that 
from  mature  animals. 

590.  Kind  of  Animal.     The  kind  of  animal,  as  has  been 
stated,  affects  the  value  per  ton  of  the  manure  more  than  it 
does  the  total  value  of  the  manure  produced  from  the  same 
feeds.     Pigs   and   cows,   however,   consume   more   food   in 
proportion  to  their  weight  than  do  horses  and  sheep,  and, 
consequently,  produce  manure  of  a  greater  total  value  dur- 
ing the  year. 

591.  Product  of  the  Animal.    Milch  cows  use  a  portion 
of  the  nitrogen  and  phosphorus  of  the  feeds  in  producing 
milk,  and  in  that  way  some  of  the  fertility  value  of  the  ma- 
nure is  lost.    The  value  of  the  plant  food  in  5000  pounds 
of  average  milk  is  $4.98. 

592.  Kind  of  Litter  Used.     Manure  consists  of  the  excre- 
ments of  animals  mixed  with  the  litter  or  bedding  material 
that  is  used  to  absorb  the  liquids.     These  materials  vary 


STABLE  MANURE 


505 


in  the  amount  of  plant  food  that  they  contain.  The  fertiliz- 
ing value  of  a  ton  of  wheat  straw  is  $2.40,  and  of  an  equal 
quantity  of  sawdust  it  is  only  $1.60. 

593.  Proportion  of  Plant  Food  Recovered  in  Manure. 
Taking  into  consideration  the  different  kinds  of  live  stock 
maintained  on  the  average  farm  and  the  proportion  of  grow-  • 
ing  and  mature  animals, 

it  may  be  assumed  that 
three  fourths  of  the 
nitrogen  and  phos- 
phoric acid  of  the  feeds 
and  over  nine  tenths  of 
the  potash  are  re- 
covered in  the  manure. 
In  a  general  way  it  may 
be  said  that  the  manure 
contains  eighty  per 
cent  of  the  fertilizing  value  of  the  ration  fed  and  the  full 
value  of  the  materials  used  for  bedding.  According  to 
these  figures  the  total  value  of  the  manure  for  a  year  from 
a  herd  of  fifty  dairy  cows  fed  a  daily  ration  of  10  pounds  of 
grain  (corn  meal,  ground  oats,  and  bran),  35  pounds  of  corn 
silage,  and  15  pounds  of  clover  hay,  and  bedded  with  wheat 
straw  amounts  to  $2,094.20. 

594.  Losses    in    Manures.     The    foregoing    statements 
refer  to  fresh  manure  which  has  suffered  no  loss  of  its  valuable 
constituents.     On  the  average  farm,  unfortunately,  because 
of  lack  of  care  in  preventing  the  losses  to  which  manure 
is  subject,  not  more  than  half  this  value  is  realized.     It  will 
be  well  to  consider  these  losses  and  the  means  by  which  they 
may  be  prevented.     The  principal  ways   in   which  plant 
food  is  lost  from  the  manure  are  as  follows :   (1)  by  neglect- 


FIG.  232.  —  Manure  pile  on  the  island  of  Jersey 
with  cistern  below  to  collect  liquid  manure. 


506 


SOILS  AND  FERTILISERS 


ing  to  save  the  liquid  manure;  (2)  by  loss  of  ammonia  in 
the  stable;  (3)  by  leaching  in  the  barnyard;  (4)  by  hot 
fermentation. 

595.  Value  of  the  Liquid  Manure.     The  liquid  part  of 
the  manure,  which  is  commonly  allowed  to  run  away,  con- 
tains two  thirds  of  the  nitrogen  and  four  fifths  of  the  potash 
excreted  by  the  animal.     The  following  table  shows  the 
distribution  of  the  plant  food  in  the  manure  from  the  fifty 
dairy  cows  mentioned  in  Section  593. 

Value  of  the  solid  part  . $716.88 

Value  of  the  liquid  part     .     ,     . 1,200.20 

Value  of  the  bedding     .     .  ;,.;.. 177.12 

Total  value  of  the  manure $2,094.20 

It  will  be  seen  that  if  the  liquid  is  lost,  the  value  of  the 
manure  will  be  less  than  $900  instead  of  $2,094.20  as 
calculated.  It  is  evident,  therefore,  that  the  stable  floors 

, .,   should     be     made     of 

cement  or  other  water- 
tight material,  and 
that  sufficient  bedding 
should  be  used  to  ab- 
sorb all  the  liquid.  In 
many  parts  of  Europe 
cisterns  are  built  in 
connection  with  the 
stables  to  collect  the 
liquid  manure ;  but  un- 
der American  conditions  it  is  best  to  keep  the  liquid  and 
solid  manures  together  by  the  plentiful  use  of  bedding. 

596.  Loss  of  Ammonia  in  the  Stable.     Manure  contains 
enormous  numbers  of  decay  bacteria  that  cause  its  rapid 
decomposition.     One  class  of  these  bacteria  liberates  am- 


FIG.  233.  —  Outfit  for  the  distribution  of 
liquid  manure  on  the  island  of  Jersey. 


STABLE   MANURE  507 

monia  from  the  liquid  manure.  Most  of  the  nitrogen  in  the 
liquid  excrement  is  in  the  form  of  an  organic  compound 
called  urea  (CON2H4).  The  bacteria  cause  the  urea  to 
take  on  water  and  change  to  ammonium  carbonate,  thus  : 

CON2H4  +  2H2O-KNH4)2CO3. 

The  ammonium  carbonate  dissociates  and  gives  off  ammonia 
and  carbon  dioxide  (164),  resulting  in  loss  of  nitrogen  from 
the  manure.  The  odor  of  ammonia  frequently  noticed  in 
the  stable  is  due  to  this  chemical  change. 

The  decomposition  does  not  take  place  so  readily  if  the 
liquid  is  completely  absorbed  by  the  bedding.  The  use  of 
dried  muck  soil  or  peat  with  the  bedding  is  effective  in  pre- 
venting this  change.  If  muck  soil  is  easily  obtained,  it  will 
pay  to  dry  a  few  wagon  loads  of  it  for  use  in  the  stable. 

Chemical  preservatives  are  sometimes  used  in  the  stable 
to  prevent  loss  of  ammonia.  The  best  material  for  this 
purpose  is  acid  phosphate  (178).  The  acid  phosphate 
unites  with  the  ammonia,  forming  the  double  salt,  calcium 
ammonium  phosphate,  which  is  not  volatile;  hence  this 
change  prevents  the  escape  of  ammonia.  The  calcium  sul- 
phate (gypsum)  which  is  always  present  in  commercial 
acid  phosphate  is  also  supposed  to  be  effective  in  preventing 
loss  of  ammonia  from  the  manure,  by  changing  the  ammo- 
nium carbonate  into  ammonium  sulphate,  which  is  not 
volatile  and  does  not  so  readily  decompose  : 


Oa  +  CaSO4  ->-  CaCO3  +  (NH4)2SO4. 

The  acid  phosphate  should  be  dusted  over  the  manure 
gutter  at  the  rate  of  one  pound  a  day  for  each  animal. 
This  use  of  acid  phosphate  is  to  be  recommended,  because, 
in  order  to  obtain  the  best  results  in  the  field,  some  phos- 


508 


SOILS  AND   FERTILIZERS 


phate  fertilizer  should  always  be  used  in  connection  with 

stable  manure  (612). 

597.  Losses  in  Manure  from  Leaching.     Next  to  improper 

absorption  of  the  liquid,  the  greatest  loss  in  manure  comes 

from  leaching  by  rains. 
As  ordinarily  handled 
the  manure  is  thrown 
out  each*  day  into  the 
open  yard  to  lie  for 
months  subjected  to 
washing  by  the  summer 
or  winter  rains.  In 


FIG.  234.  —  Great  losses  result  from  leaving 
manure  exposed  to  the  weather. 


many  cases  it  is  even 
deposited  under  the 
eaves  of  a  large  barn, 
and  thus  ,  the  washing 

process  is  made  more  complete.  It  is  absurd  to  go  to  the 
trouble  of  absorbing  all  the  liquid  excrement  by  means  of  bed- 
ding, and  then  allow  it  to  be  washed  out  of  the  manure.  The 
losses  in  manure  due  to  leaching  by  rains  in  the  open  yard 
are  much  greater  than  most  people  imagine.  Many  experi- 
ments have  been  carried  on  to  determine  these  losses,  and 
the  following  table  gives  the  results  of  four  such  experiments : 

LOSSES  IN  MANURE  FROM  LEACHING 


PERIOD 
Days 

NITROGEN 
Per  Cent 

PHOSPHORIC  ACID 
P205 
Per  Cent 

POTASH 
K2O 
Per  Cent 

131 

57.0 

62.0 

72.0 

70 

44.0 

16.0 

28.0 

76 

39.0 

63.0 

56.0 

50 

69.0 

59.0 

72.0 

Average 

•     52.2 

50.0 

57.0 

STABLE  MANURE 


509 


The  table  shows  that  the  average  loss  amounted  to  more 
than  half  the  plant  food  in  the  manure  during  rather  short 
periods,  the  longest  time  being  a  little  over  four  months. 

On  many  farms  the  manure  is  exposed  to  the  weather  for 
a  much  longer  period  of  time.  These  losses  vary  with  the 
climatic  conditions  and  with  the  quality  of  the  rations. 
During  heavy  rains,  especially  if  they  occur  in  warm  weather, 
the  losses  are  much  greater  than  in  dry  or  cold  weather. 
In  the  experiments  noted  above,  the  rainfall  was  as  great 
during  the  50  days  of  the  last  experiment  as  it  was  in  the 
case  of  the  131  days  of  the  first  one.  The  relative  decrease 
in  value  is  larger  for  manures  produced  from  rations  of  high 
nutritive  value.  In  other  words,  the  more  valuable  the 
manure,  the  greater  will 
be  the  percentage  of 
loss  from  leaching.  It 
is  conservative  to  say 
that  manure  exposed 
to  the  weather  for  six 
months  loses  fully  half 
its  value. 

It  is  worthy  of  note 
also  that  the  plant  food 
that  is  washed  out  of 
the  manure  is  the  part 
that  is  most  available, 
as  it  is  soluble  in  water  and  is  in  the  condition  in  which  it 
can  be  immediately  used  by  the  plants.  The  manure  that 
remains,  on  the  other  hand,  represents  the  tougher  and  more 
slowly  decomposed  material,  hence  it  contains  the  least 
available  part  of  the  plant  food. 

Manure  is  never  so  valuable  as  when  perfectly   fresh. 


FIG.  235.  —  Covered  manure  shed  with  cemented 
bottom. 


510  SOILS  AND   FERTILIZERS 

Even  the  best  methods  of  handling  and  care,  if  the  manure 
is  stored,  cannot  prevent  more  or  less  loss  of  the  valuable 
constituents.  For  this  reason  it  is  advisable  to  haul  the 
manure  directly  from  the  stable  to  the  field  each  day,  when- 
ever the  conditions  permit. 

There  are  always  times  on  every  farm  when  it  is  not 
possible  to  haul  the  manure  directly  to  the  field,  and  some 

suitable  place  should 
be  provided  for  its 
temporary  storage  (Fig. 
235).  The  essential 
requisite  of  such  a 
storage  place  is  that 
it  shall  have  a  cemented 
bottom  to  prevent  any 
loss  of  the  liquid  ma- 

FIG.  236.  —  Cattle  in  a  covered  barnyard. 

nure.  A  cover  to  pro- 
tect it  from  the  rains  is  desirable.  A  small  manure  shed 
would  pay  for  itself  in  a  single  season  on  a  farm  maintaining 
much  live  stock. 

Some  farmers  store  the  manure  in  what  is  called  a  covered 
barnyard  (Fig.  236),  which  is  usually  one  large  room  in  the 
barn  in  which  the  cattle  are  allowed  to  run  during  the 
greater  part  of  the  day.  The  floor  is  cemented  and  bedding 
material  is  liberally  used.  The  cattle  tramp  the  manure 
into  a  solid  mass  and  it  is  allowed  to  accumulate  until  it  is 
convenient  to  remove  it  to  the  field.  Protected  in  this  way, 
the  manure  suffers  very  little  loss  of  fertilizing  constituents. 

598.  Open  Yard  Feeding  a  Wasteful  Practice.  It  is 
probably  true  that  upon  a  majority  of  the  farms  in  America 
cattle  are  fed  during  the  winter  in  open  lots,  the  manure 
not  being  hauled  away  until  the  following  summer  or  fall, 


STABLE   MANURE 


511 


if  indeed  it  is  removed  at  all.  This  method  of  feeding  pre- 
sents conditions  that  result  in  excessive  losses  from  leaching, 
and  it  is  safe  to  say  that  more  than  half  the  fertilizing  value 
of  the  manure  is  lost  where  this  practice  is  followed.  In 
the  corn  .belt  of  this  country,  for  instance,  large  numbers 
of  cattle  are  fed  during  the  winter,  and  it  is  not  unusual 
to'  see  a  large  feeding 
lot  covered  to  a  con- 
siderable depth  with 
manure  which  is  spread 
out  and  exposed  to  the 
weather  in  such  a  way 
that  the  maximum  ef- 
fects of  leaching  must 
take  place.  There  is 
no  doubt  that,  con- 
sidered from  the  fertility 
point  of  view  alone, 
these  farms  would  be  better  off  if  the  corn  were  sold  from 
the  farm  and  the  stover  plowed  under.  The  feeding  of  the 
future  must  be  done  under  cover  if  the  fertility  of  the  soil  is 
to  be  economically  maintained. 

599.  Hot  Fermentation.  Manure  that  has  been  thrown 
into  a  loose  heap,  especially  if  it  contains  much  horse  or 
sheep  manure,  soon  becomes  very  hot.  The  heating  some- 
times proceeds  so  far  that  part  of  the  manure  becomes  white, 
or  fire-fanged  as  it  is  popularly  called.  An  examination 
will  show  that  ammonia  is  being  evolved  in  large  quantities 
from  the  heating  manure.  This  fermentation  is  caused  by 
certain  bacteria  that  bring  about  oxidation  of  the  organic 
matter,  the  nitrogen  being  converted  into  ammonia.  The 
loss  of  nitrogen  in  this  way  is  very  large,  the  amount  vary- 


FlG.  237.  —  Open  yard  feeding  greatly  reduces 
the  fertilizing  value  of  manure. 


512  SOILS  AND  FERTILIZERS 

ing  in  different  experiments  from  20  per  cent  to  over  80  per 
cent.  In  the  case  of  the  white  fire-fanged  material  all 
the  nitrogen  is  driven  off.  Since  the  bacteria  that  cause 
this  rapid  oxidation  of  the  organic  matter  cannot  exist  in 
the  absence  of  free  oxygen,  no  heating  will  take  place  if  the 
manure  pile  is  so  compact  that  no  air  can  enter  it.  In  a 
moist,  compact  manure  pile  a  cold  fermentation  takes  place, 
which  is  caused  by  an  entirely  different  class  of  bacteria 
and  which  does  not  result  in  the  formation  and  loss  of  am- 
monia. It  is  evident,  therefore,  that  the  stored  manure 
should  be  carefully  compacted  as  well  as  protected  from 
leaching.  It  will  be  seen  that  the  covered  barnyard  presents 
almost  ideal  conditions  for  storing  manure.  A  method  of 
storage  very  similar  to  the  covered  barnyard  plan  has  been 
in  use  in  Europe  for  many  years  and  is  known  as  the  deep 
stall  method.  The  manure  accumulates  in  the  stall  in  such 
a  way  that  it  is  thoroughly  packed  by  the  feet  of  the  cattle, 
and  is  said  to  lose  very  little  of  its  fertilizing  value. 

600.  Composting  Manures.  Any  method  of  storing 
manure  requires  considerable  labor,  and  for  that  reason 
storing  it  is 'to  be  avoided  in  general  farming  whenever  it  is 
possible  to  use  it  in  the  fresh  condition.  In  market  garden- 
ing, on  the  other  hand,  such  quantities  of  manure  are  used 
that  it  is  necessary  to  have  it  thoroughly  rotted  before 
applying,  as  otherwise  the  crop  would  suffer  from  the  heat- 
ing effect  that  the  large  amount  of  raw  manure  would  have 
on  the  soil.  While  the  manure  may  be  rotted  by  keeping 
it  in  a  moist,  compact  heap,  it  must  be  remembered  that  the 
manure  commonly  used  by  market  gardeners  is  the  horse 
manure  from  the  city  stables.  This  heats  so  rapidly  that 
special  care  is  necessary  to  prevent  hot  fermentation,  and 
the  pile  must  be  moistened  frequently. 


STABLE  MANURE  513 

Many  market  gardeners  prefer  to  compost  the  manure 
with  earth,  peat,  or  muck.  This  is  done  by  making  a  founda- 
tion of  about  six  inches  of  dirt  and  placing  on  top  of  this 
alternate  layers  of  manure  and  soil,  moistening  the  mass  as 
the  heap  grows.  The  sides  and  the  top  should  be  smoothed 
off  and  the  mass  covered  with  a  thin  layer  of  earth  to 
prevent  loss  of  nitrogen.  After  about  two  months  the 
pile  should  be  turned  over,  the  materials  thoroughly 
mixed,  and  more  water  added,  if  necessary,  to  keep  the 
compost  moist.  A  compost  in  great  favor  with  green- 
house men  is  one  made  of  manure  and  sod,  these  materials 
bsing  piled  in  alternate  layers  as  described  above.  This 
gives  the  fibrous  compost  so  desirable  for  bench  and  pot 
work. 

Any  of  the  refuse  organic  materials  of  the  farm  or  garden 
may  be  used  in  composts.  Weeds,  refuse  parts  of  plants, 
dead  animals,  and  kitchen  wastes  may  be  added  to  the 
manure-earth  mixture,  or  composted  separately ;  for  handled 
in  this  way  they  decompose  rapidly  and  without  offensive 
odors.  The  presence  of  the  earth  decreases  the  loss  of  am- 
monia where  highly  nitrogenous  materials  are  used.  In 
using  composts  a  good  practice  is  to  add  bone  meal  to  the 
heap.  In  this  way  the  plant  food  in  the  bone  meal  is 
made  available  to  the  plants,  and  the  compost  is  made  more 
valuable. 

601.  Applying  Manure.  Two  general  methods  for  the 
application  of  manure  are  in  common  use :  one  is  to  throw 
it  into  heaps,  where  it  is  allowed  to  remain  some  time  before 
being  spread ;  the  other  is  to  broadcast  it  directly  from  the 
wagon.  The  first  method  is  objectionable  for  several  rea- 
sons. In  the  first  place  it  increases  the  work  necessary  to 
spread  the  manure,  since  it  must  be  handled  twice,  and  it 

EV.   CHEM. 33 


514  SOILS  AND  FERTILIZERS 

takes  no  more  labor  to  spread  it  from  the  wagon  than  from 
the  heap  on  the  ground.  The  leachings  from  these  heaps 
make  the  'spots  directly  beneath  more  fertile  than  the  rest 
of  the  field,  and  hence  produce  a  rank  growth  at  those 
places  (Fig.  238).  This  uneven  growth  is  undesirable,  be- 
cause in  the  case  of  grains  it  increases  the  danger  of  lodging 
in  the  more  fertile  spots ;  and  in  any  case  it  results  in  un- 
evenness  in  the  maturity  of  the  crop.  A  crop  that  has  a  large 
supply  of  plant  food,  for  instance,  has  a  longer  period  of 


FIG.  238.  —  Showing  the  uneven  growth  due  to  allowing  manure  to  remain 
in  heaps  before  spreading. 

growth  than  one  with  a  meager  supply  and  consequently  is 
later  in  maturing.  If,  therefore,  the  field  is  very  uneven  in 
fertility,  a  part  of  the  crop  will  be  ready  to  harvest  some 
time  before  the  rest  has  matured.  On  the  other  hand,  if  the 
manure  is  spread  directly  from  the  wagon,  not  only  is  the 
labor  lessened,  but  the  danger  of  unevenness  in  growth  is 
to  some  extent  avoided.  Moreover  there  is  no  likelihood  of 
loss  in  the  value  of  the  manure  when  it  is  spread  in  a  thin 
layer  on  the  ground. 

Manure  spreaders  (Fig.  239)  are  coming  into  general  use. 
Some  recent  experiments  seem  to  indicate  that  manure  gives 


STABLE   MANURE 


515 


FIG.  239.  —  The  best  way  to  apply  manuie  is 
by  means  of  the  manure  spreader. 


better  returns  when  spread  by  the  machine  than  it  does 
when  applied  by  hand.  Whatever  method  is  used  to  spread 
the  manure,  it  will  readily  be  seen  that  the  finer  the  material 
the  easier  it  will  be  to 
distribute  it  evenly. 

602.  Where    to  Use 
Manure.    There  is  some 
difference  of  opinion  as 
to  which  of  the  ordinary 
farm  crops  give  the  best 
returns   for  the  use  of 
stable   manure.     Prob- 
ably more   farmers  use 
it  on  the  land  plowed 
for   corn   than   in   any 

other  way.  Corn  is  especially  adapted  to  utilize  the  plant 
food  of  manure,  since  it  makes  the  greater  part  of  its  growth 
in  midsummer,  when  nitrification  is  at  its  height  and  the 
nitrogen  of  the  manure  is  being  made  available  most  rapidly. 
It  is  always  safe  to  manure  corn  heavily. 

Many  farmers  prefer  to  use  manure  as  a  top  dressing  for 
grass  lands,  since  such  use  increases  the  organic  matter  of 
the  soil  by  stimulating  the  growth  of  the  fibrous  roots  of  the 
sod.  This  method  gives  good  returns  for  the  manure  used. 
The  permanent  pastures  should  not  be  neglected,  but  should 
be  occasionally  top  dressed  with  manure  and  commercial 
fertilizers. 

603.  Amount    to    Apply.     Market    gardeners    use    very 
large  quantities  of  manure,  sometimes  as  much  as  forty 
tons  to  the  acre,  but  they  probably  use  the  manure  for  its 
physical  effect  upon  the  soil  even  more  than  for  the  plant 
food  that  it  contains.    This  is  partly  due  to  the  fact  that 


516  SOILS  AND  FERTILIZERS 


the  gardener  cannot  conveniently  make  extended  use  of 
green  manures  as  a  source  of  organic  matter.  For  ordinary 
farm  crops,  on  the  other  hand,  it  is  not  customary  to  use 
more  than  eight  to  ten  tons  to  the  acre,  and  on  general 
principles  it  may  be  stated  that  somewhat  frequent  light 
dressings  pay  better  than  very  large  ones  given  at  long  inter- 
vals. On  the  other  hand,  the  amount  of  manure  produced 
on  the  average  farm  is  so  small  when  compared  with  the 
land  to  be  fertilized  that  it  would  be  impossible  to  spread 
it  over  all  the  farm  yearly.  For  this  reason,  it  is  a  good 
plan  to  apply  the  manure  to  one  or  two  crops  in  the  rota- 
tion, thus  covering  only  a  part  of  the  farm  each  year. 

604.  How  Manure  Improves  Soils.     Stable  manure  adds 
all  the  elements  of  plant  food  to  the  soil,  and  while  some  of 
it  is  not  in  forms  immediately  available  to  the  plant  it 
becomes  so  during  a  period  of  years.     Manure  adds  to  the 
soil  enormous  numbers  of  bacteria  that  attack  not  only 
the  manure  itself  but  the  organic  matter  already  in  the  soil. 
Manure  also  improves  the  physical  condition  of  the  soil, 
and  during  its  decay  the  acid  products  formed  act  upon 
the  potential  plant  food  and  make  some  of  it  available. 
Attention  has  already  been  called  to  the  fact  that  when 
properly  handled  the  manure  returns  to  the  soil  nearly  one 
half  the  organic  matter  of  the  feeds.     Everything  considered, 
manure  is  probably  the  best  fertilizer  the  farmer  can  use, 
especially  when  it  is  reenforced  with  acid  phosphate. 

605.  Results  with  Manure.     The  good  results  in  crop 
yields  from  the  use  of  stable  manure  are  known  to  every 
farmer  and  gardener.     In  one  experiment  in  England  the 
use  of  manure  has  maintained  the  yield  of  wheat  at  34 
bushels  to  the  acre  for  seventy-five  years,  while  the  average 
for  the  unmanured  field  was  only  13  bushels.     At  the  Ohio 


STABLE   MANURE 


517 


FIG.  240.  —  The  field  on  the  left  received  ten 
tons  of  manure  while  the  one  on  the  right  was 

unmanured. 


Experiment  Station  stable  manure  has  given  a  profit  in 
increased  yields  of  $3.22  for  each  ton  of  manure  used  over 
a  period  of  twenty  years. 
Manure  differs  from 
other  fertilizers  in  its 
lasting  effects  when  ap- 
plied to  the  soil.  In 
one  experiment  manure 
was  used  on  a  plot 
for  twenty  years,  after 
which  ks  use  was  dis- 
continued. The  gooi 
effect  was  noticeable  for 
more  than  thirty  years  after  the  last  application.  Every 
farmer  knows  that  the  effects  of  a  single  application  of  manure 
are  evident  five  or  six  years  after  its  use. 

606.  City  Sewage.  Large  quantities  of  plant  food  are 
lost  in  the  sewage  of  the  cities.  City  sewage  contains  nitro- 
gen, phosphorus,  and 
potassium  to  the  annual 
value  of  one  dollar  for 
each  inhabitant.  In 
China  and  Japan,  two 
countries  noted  for  their 
high  crop  production, 
the  sewage  of  the  cities 
has  been  used  as  a  fer- 
tilizer for  thousands  of 
years.  The  sewage  is 
carried  out  to  the  farms 
and  gardens,  diluted  with  water,  and  used  on  the  growing 
crops.  Such  a  procedure  is  repulsive  to  the  occidental  mind ; 


FIG.  241.  —  Using  city  sewage  as  a  fertilizer 
in  Japan. 


518  SOILS  AND  FERTILIZERS 

but  it  would  be  a  great  thing  for  agriculture  if  some  unob- 
jectionable method  could  be  discovered  to  make  use  of  the 
large  amount  of  plant  food  now  being  lost  in  the  city  sewage. 

EXERCISES 

Ex.  364.  Is  the  use  of  stable  manure  as  a  fertilizer  of  recent  or 
ancient  origin?  What  is  the  value  of  the  manure  produced  annually 
in  the  United  States  ?  Is  much  of  this  value  lost  ?  Why  is  a  well- 
kept  manure  heap  an  indication  of  thrift  ?  How  is  the  value  of  manure 
stated  ?  What  is  meant  in  trade  by  phosphoric  acid  ?  By  potash  ? 

Ex.  365.  How  do  the  values  of  the  manure  from  different  kinds 
of  animals  compare  ?  Which  is  the  most  valuable  per  ton  ?  To  what 
is  this  difference  in  value  per  ton  largely  due  ?  Is  there  much  difference 
in  the  total  value  of  the  manure  produced  by  the  different  animals 
from  the  same  feeds  ? 

Ex.  366.  What  are  the  five  factors  affecting  the  value  of  fresh 
manures?  Explain  how  the  value  of  the  manure  is  affected  by  the 
kind  of  feeds ;  by  the  age  of  the  animal ;  by  the  kind  of  animal ; 
by  the  animal  products ;  by  the  kind  of  litter.  What  proportion  of 
the  plant  food  in  the  ration  is  recovered  in  the  manure  ? 

Ex.  367.  If  fifty  animals  were  fed  the  ration  given  on  page  336, 
what  would  be  the  value  of  the  manure  produced  in  a  year,  assuming 
that  ten  pounds  of  wheat  straw  were  used  daily  as  bedding  for  each 
animal?  (For  the  fertilizing  constituents  of  the  feeds  and  bedding 
see  tables  in  Vivian's  First  Principles  of  Soil  Fertility.) 

Ex.  368.  In  what  four  principal  ways  is  plant  food  lost  from  the 
manure?  What  proportion  of  the  different  elements  of  plant  food  is 
found  in  the  liquid  manure  ?  In  the  solid  manure  ?  What  proportion 
of  the  value  of  the  manure  is  lost  if  the  liquid  is  not  saved  ? 

Ex.  369.  In  what  form  is  the  nitrogen  in  the  liquid  excrement? 
What  compound  do  the  bacteria  form  from  the  urea?  Write  the 
reaction.  To  what  is  the  odor  of  ammonia  in  stables  due  ?  How  may 
the  loss  of  ammonia  in  the  stable  be  prevented?  Write  the  equation 
for  the  reaction  between  gypsum  and  ammonium  carbonate.  How 
should  acid  phosphate  be  used  to  prevent  loss  of  ammonia  ? 

Ex.  370.  How  much  of  the  plant  food  is  lost  when  manure  is  ex- 
posed to  the  weather  ?  How  do  climatic  conditions  affect  the  amount  of 


STABLE  MANURE  519 

loss?  Explain  the  statement  that  the  most  available  part  of  the  plant 
food  is  lost  by  leaching.  Why  should  manure  be  hauled  directly  to  the 
field  when  possible?  What  are  the  essentials  of  a  storage  place  for 
manure  ?  What  is  meant  by  a  covered  barnyard  ?  Is  there  much  loss 
in  manure  stored  in  a  covered  barnyard  ?  Are  there  any  farms  in  your 
neighborhood  where  manure  is  being  wasted?  Do  any  of  the  farms 
near  the  school  have  manure  sheds  or  covered  barnyards  ? 

Ex.  371.  Explain  why  open  yard  feeding  is  wasteful  of  manure. 
What  is  meant  by  L  Dt  fermentation  of  manure  ?  What  losses  occur 
from  hot  fermentation  ?  How  may  hot  fermentation  be  prevented  ? 
What  is  meant  by  composting  manure  ?  How  is  a  compost  heap  pre- 
pared ?  What  other  materials  beside  manure  may  be  composted? 

Ex.  372.  Why  should  manure  never  be  placed  in  heaps  on  the 
field  before  spreading?  Why  is  a  manure  spreader  desirable  on  a 
farm  ?  Upon  what  crop  is  manure  most  commonly  used  ?  What 
crops  do  the  farmers  of  your  locality  manure  ?  Why  does  corn  re- 
spond so  well  to  treatment  with  stable  manure  ?  What  are  the  advan- 
tages of  using  manure  on  grass  lands? 

Ex.  373.  How  much  manure  is  used  to  the  acre  by  market  gar- 
deners? In  ordinary  farming?  Which  is  the  more  desirable,  heavy 
applications  at  long  intervals  or  frequent  light  applications?  Explain 
how  manure  improves  the  soil.  Discuss  the  lasting  effect  of  manure. 
How  much  plant  food  is  lost  in  city  sewage?  In  what  countries  is 
the  city  sewage  all  saved  and  used  on  the  crops  ? 


CHAPTER  LIX 
COMMERCIAL  SOURCES   OF  PLANT  FOOD 

PHOSPHORUS 

607.  Phosphorus  must  be  Purchased.  Phosphorus  is  the 
one  element  that  must  be  purchased  on  practically  every 
farm  if  its  fertility  is  to  be  maintained.  It  is  the  element 
that  is  the  limiting  factor  on  nearly  every  farm.  Phosphorus 
is  present  in  small  quantities,  some  of  the  soils  containing 
as  little  as  0.01  per  cent  and  very  few  having  as  much  as 
0.15  per  cent.  From  two  thirds  to  three  fourths  of  the 
phosphorus  taken  from  the  soil  by  the  plants  is  stored  in 
the  seeds,  and  is,  therefore,  removed  from  the  farm  when 
grain  is  sold.  Animals  use  phosphorus  in  making  bone 
and  milk ;  hence  the  sale  of  milk  or  live  stock  also  removes 
phosphorus  from  the  farm.  While  the  loss  of  phosphorus 
from  the  sale  of  animal  products  is  much  less  than  that 
from  the  sale  of  the  crops,  it  is  sufficiently  large  to  be  a 
decided  drain  on  the  phosphorus  supply  of  the  soil,  especially 
if  the  manure  produced  by  the  animals  does  not  receive 
better  care  than  is  given  to  it  on  the  average  farm.  There 
is  no  natural  method  of  increasing  the  phosphorus  of  the  soil, 
such  as  there  is  in  the  case  of  nitrogen,  by  the  fixation  due 
to  the  nodule-forming  bacteria.  The  farmer,  therefore, 
must  purchase  phosphorus  to  replace  that  which  is  removed 
from  the  farm. 

When  feeds  are  purchased  in  large  quantities,  as  they  are 
on  some  dairy  farms,  phosphorus  is  brought  on  to  the  farm 

520 


COMMERCIAL  SOURCES  OF  PLANT  FOOD       521 

in  them  and  may  be  put  into  the  soil  through  the  manure. 
In  this  case,  however,  much  more  nitrogen  than  phosphorus 
is  purchased,  and  additional  phosphorus  is  necessary  if 
maximum  yields  are  to  be  obtained.  Recent  investigations 
make  it  clear  that  a  certain  balance  between  the  elements  of 
plant  food  in  the  soil  is  essential  to  the  best  results  in  plant 
growth.  In  other  words,  a  balanced  ration  for  plants  is 
quite  as  desirable  as  a  balanced  ration  for  animals. 

608.  Bone  Phosphates.  The  commercial  sources  of 
phosphorus  for  fertilizers  are  the  bones  of  animals  and  the 
various  deposits  of  mineral  phosphates;  and,  as  has  been 
mentioned,  the  phosphorus  is  stated  in  fertilizer  trade  not 
as  the  element,  but  as  phosphoric  acid  (P2O5).  The  bones 
of  animals  have  been  used  as  fertilizers  for  several  centuries, 
and  many  farmers  still  prefer  them  to  any  other  form  of 
phosphorus  fertilizers.  The  mineral  matter  of  bone  consists 
almost  entirely  of  tricalcium  phosphate,  which  is  thoroughly 
permeated  by  the  organic  matter  of  the  bone.  The  bones 
used  in  making  fertilizers  come  from  the  packing  houses, 
and  from  the  reducing  establishments  which  use  the  animals 
that  die  from  accident  or  disease. 

Before  being  used  as  a  fertilizer  the  bones  are  ground  to  a 
fine  powder.  If  they  are  ground  in  the  natural  condition, 
the  powder  *is  known  as  raw  bone  meal;  if  they  are  ground 
after  they  have  been  steamed  to  remove  the  fat,  the  product 
is  steamed  bone  meal.  Raw  bone  meal  contains  about 
22  per  cent  of  phosphoric  acid  (9.5  per  cent  phosphorus) 
and  4  per  cent  of  nitrogen,  while  steamed  bone  meal  con- 
tains about  28  per  cent  of  phosphoric  acid  (12  per  cent 
phosphorus)  and  2  per  cent  of  nitrogen  (179). 

The  steamed  bone  meal  is  the  better  product  to  use,  since 
it  contains  more  phosphorus  and  is  more  readily  decomposed 


522  SOILS  AND   FERTILIZERS 

in  the  soil.  The  fat  in  the  raw  bones  interferes  with  the 
decay  of  the  bone  and  has  itself  no  fertilizing  value, 
but  can  be  used  to  advantage  in  other  ways.  Steamed 
bone  meal,  too,  is  usually  lower  in  price  than  the  raw 
bone  meal. 

609.  Mineral  Phosphates.  Deposits  of  tricalcium  phos- 
phate are  found  in  several  places  in  this  country  and  in 
Canada.  Most  of  that  used  in  fertilizers  at  the  present 
time  comes  from  Tennessee,  South  Carolina,  and  Florida. 
The  mineral  phosphate  has  the  same  chemical  composi- 
tion as  that  found  in  the  mineral  matter  of  bones,  but 
since  it  is  not  permeated  with  organic  matter,  as  is  the  bone 
phosphate,  it  is  less  soluble  in  the  soil  moisture  than  is  the 
other. 

There  is  some  difference  of  opinion  as  to  whether  plants 
can  utilize  the  phosphorus  of  the  rock  phosphates  even  when 
the  material  is  finely  ground.  It  is  generally  agreed  that 
these  phosphates  are  of  practically  no  value  when  used  on 
soils  that  are  very  low  in,  organic  matter ;  but  it  is  held  by 
many  that  when  mixed  with  manure  or  turned  under  with 
clover  or  other  green  manure  crops  they  are  valuable  sources 
of  phosphorus.  The  theory  has  been  advanced  that  the 
carbon  dioxide  evolved  by  the  decaying  organic  matter 
makes  enough  of  the  phosphate  soluble  to  supply  the  needs 
of  the  growing  crop.  The  advocates  of  rock  phosphate 
recommend  that,  as  the  material  is  comparatively  cheap, 
it  be  applied  in  large  quantities  (1000  pounds  or  more  every 
four  years)  with  a  green  manure  crop,  and  that  the  soil  be 
kept  well  supplied  with  organic  matter. 

The  finely  ground  rock  phosphate  is  known  in  some 
sections  of  the  country  as  floats.  A  good  sample  contains  at 
least  28  per  cent  of  phosphoric  acid,  but  as  the  rock  phos- 


COMMERCIAL  SOURCES  OF  PLANT  FOOD       523 

phates  vary  greatly  in  purity,  floats  should  be  purchased  only 
on  a  guaranteed  analysis. 

610.  Acid  Phosphate.  It  has  long  been  the  custom  to 
treat  the  rock  phosphates  with  sulphuric  acid  to  make  the 
phosphorus  more  available.  The  proportions  of  acid  and 
phosphate  used  should  be  such  as  to  convert  the  tricalcium 
phosphate  into  monocalcium  phosphate  (176  and  178),  thus  : 

Ca3(P04)2  +  2  H2S04  -^  CaH4(P04)2  +  2  CaSO4. 

The  monocalcium  phosphate  is  soluble  in  water  and  hence 
is  available  for  plant  growth.  The  soluble  phosphate  is  not 
separated  from  the  calcium  sulphate,  but  the  whole  mixture 
resulting  from  the  treatment  of  the  rock  phosphate  with  the 
acid  is  sold  under  the  different  names  of  acid  phosphate, 
superphosphate,  and  acidulated  rock. 

If  not  enough  acid  is  used  to  convert  all  the  phosphate 
into  the  monocalcium  form,  the  following  reaction  may 
take  place : 

Ca3(PO4)2  +  CaH4(PO4)2  ->-  2  Ca2H2(PO4)2. 

This  new  compound  is  dicalcium  phosphate,  and  as  it  is 
regarded  as  an  intermediate  step  in  the  reversion,  or  changing 
back,  of  monocalcium  to  tricalcium  phosphate,  it  is  known 
in  the  trade  as  reverted  phosphate.  Dicalcium  phosphate  is 
not  soluble  in  water,  but  is  readily  dissolved  by  very  weak 
acids  and  is  supposed  to  be  as  available  to  the  plants  as  the 
monocalcium  phosphate.  For  that  reason  the  phosphoric 
acid  of  these  two  compounds,  monocalcium  and  tricalcium 
phosphates,  is  termed  available  phosphoric  acid. 

Acid  phosphates  as  found  on  the  market  contain  from 
12  to  18  per  cent  of  available  phosphoric  acid  (P2O5)  in 
the  two  forms  of  monocalcium  phosphate  and  dicalcium 


524 


SOILS  AND  FERTILIZERS 


phosphate.  In  all  probability  more  phosphorus  is  purchased 
by  farmers  in  the  form  of  acid  phosphate  than  in  all  other 
materials  combined. 

611.  Basic  slag  is  used  in  large  quantities  in  Europe  and 
to  some  extent  in  this  country  as  a  source  of  phosphorus 
for  plant  food.     It  is  made  from  certain  European  iron  ores 
that  contain  considerable  quantities  of  phosphorus  (236). 
Basic  slag  contains  about  18  per  cent  of  phosphoric  acid  in 
a  form  that  is  readily  available  to  the  crops. 

612.  Phosphates  with  Manure.    A  ton  of  average  stable 
manure  contains  about  9  pounds  of  nitrogen,  2  pounds  of 


FIG.  242.  —  Showing  the  increase  in  yield  from  one  ton  of  manure.  1.  Yard 
manure.  2.  Stable  manure.  3.  Stable  manure  with  forty  pounds  of  floats. 
4.  Stable  manure  with  forty  pounds  of  acid  phosphate. 

phosphorus,  and  8  pounds  of  potassium.     Manure,  therefore, 
is  evidently  deficient  in  phosphorus,  and  it  is  not  surprising 
that  the  addition  of  a  phosphate  to  it  materially  increases 
its  crop-producing  power. 
At  the  Ohio  Station  an  experiment  has  been  running  for 


COMMERCIAL  SOURCES  OF  PLANT  FOOD       525 

twenty  yea  s  in  which  stable  manure  alone  has  been  compared 
with  manuies  to  which  acid  phosphate  and  floats  have  been 
added.  All  manures  were  used  at  the  rate  of  eight  tons  to 
the  acre  on  the  corn  in  a  three-year  rotation  of  corn,  wheat, 
and  clover.  In  one  case  forty  pounds  of  acid  phosphate  and 
in  another  forty  pounds  of  floats  were  added  to  each  ton  of 
manure.  As  an  average  for  the  entire  period  the  stable 
manure  alone  gave  an  increase  of  crops  worth  $3.22  for 
each  ton  of  manure.  A  ton  of  stable  manure  and  forty 
pounds  of  floats  gave  a  net  profit  of  $4.56,  and  a  ton  of 
manure  and  forty  pounds  of  acid  phosphate  gave  a  net  profit 
of  $4.80.  It  will  probably  always  pay  to  add  some  form  of 
phosphate  to  the  manure,  and  the  best  way  to  use  it  is  to 
scatter  it  over  the  manure  in  the  stable.  Floats  do  not 
have  the  power  of  fixing  ammonia  that  was  noted  in  the 
case  of  acid  phosphate  (596). 

POTASSIUM 

613.  Need  of  Potassium.  Most  soils  are  more  abundantly 
supplied  with  potassium  than  with  phosphorus,  and  for 
that  reason  potassium  is  less  frequently  the  limiting  factor 
of  plant  growth.  Fully  three  fourths  of  the  potassium  of 
the  mature  crop  is  found  in  the  stems  and  the  leaves,  which 
are  not  so  generally  sold  from  the  farm  as  are  the  seeds. 
Likewise  the  animal  retains  very  little  of  the  potassium 
of  its  food ;  hence  most  of  the  potassium  of  the  ration  is 
recovered  in  the  manure. 

In  the  case  of  peat  soils  and  some  sandy  soils,  however, 
potassium  is  the  limiting  factor  and  it  must  be  supplied 
to  make  them  productive.  Some  plants,  such  as  tobacco, 
potatoes,  and  cabbage,  require  large  quantities  of  potassium, 


526  SOILS  AND   FERTILIZERS 

and  their  successful  culture  for  long  periods  on  most  soils 
necessitates  the  use  of  some  commercial  form  of  potassium. 

614.  Potassium    Salts.     For  many  years  practically  all 
the  potash  used   in  fertilizing  came  from  the  European 
potash  mines.    These  mines  contain  immense  deposits  of 
salts,  containing  various  percentages  of  potash.     Only  three 
or  four  of  these  products  have  been  commonly  used  in  this 
country  and  they  are  the  only  ones  that  will  be  discussed  here. 

615.  Kainit.     This  is  one  of  the  crude  salts  which  has 
been  ground  to  a  powder.     It  looks  somewhat  like  com- 
mon salt,  but  is  darker  in  color  and  contains  about  12.5 
per  cent  of  potash  (K2O)  in  the  form  of  sulphate,  mixed 
with  sulphate  and  chloride  of  magnesium. 

616.  Muriate  of  potash  is  manufactured  from  the  crude 
minerals  of  the  mines  by  concentration,  and  contains  about 
50  per  cent  of  potash  in  the  form  of  potassium  chloride.    At 
the  present  price  the  muriate  supplies  potash  at  a  cheaper 
price  than  any  of  the  other  materials. 

617.  Sulphate  of  potash  is  another  concentrated  product 
of   the   European  mines.     What  is   known  as   high-grade 
sulphate  contains  about  53  per  cent  of  potash  in  the  form  of 
the  sulphate  (K2S04).    The  actual  potash  in  this  compound 
costs  a  trifle  more  per  pound  than  in  the  muriate.     A  lower 
grade   sulphate   containing  26   per   cent   of  potash  mixed 
with  magnesium  sulphate  is  sold  under  the  name  of  double 
manure  salt. 

A  relatively  small  quantity  of  potash  is  produced  from 
the  ash  of  the  giant  kelps  which  are  S3  abundant  on  the 
Pacific  coast.  There  are  also  certain  alkali  lakes  in  this 
country  from  which  some  potash  is  obtained,  notably 
those  in  Nebraska.  The  potash  (K2O)  produced  from  these 
lakes  in  1917  was  about  20,000  tons,  while  the  amount 


COMMERCIAL  SOURCES  OF  PLANT  FOOD       527 

annually  used  in  this  country  previous  to  1914  was  nearly 
300,000  tons. 

618.  Wood  ashes  at  one  time  were  the  sole  source   of 
potash  for  fertilizing  purposes,  but  at  present  ashes  supply 
only  a  very  small  proportion  of  this  element  of  plant  food. 
Wood  ashes  vary  greatly  in  composition,  the  ash  from  soft 
woods  containing  less  potash  than  that  from  hard  woods, 
the  content  of  potash  ranging  from  2  to  8  per  cent.     Potash 
as  found  in  wood  ashes  is  in  a  form  that  is  very  soluble 
in  water;    so  that  ashes  exposed  to  the  weather  may  have 
practically   all   the    potash    leached    out    of   them    (204). 
Leached  ashes  as  a  rule  contain  less  than  2  per  cent  of  potash. 
As  it  is  not  possible  to  distinguish  between  leached  and  un- 
leached  ashes  by  mere  physical  examination,  it  is  evident  that 
this  material  should  be  purchased  only  from  guaranteed 
analysis. 

NITROGEN 

619.  Importance   of  Nitrogen.     In  some  ways  nitrogen 
is  the  most  important  element  of  plant  food.     The  more 
common  farm  crops  use  more  nitrogen  than  they  do  phos- 
phorus  and   potassium   combined.     Nitrogen   is   the   most 
expensive  fertilizing  material  to  buy,  as  it  costs  about  three 
times  as  much  a  pound  as  either  phosphorus  or  potassium. 
It  is,  unfortunately,  more  easily  lost  from  the  farm  than 
any  other  element  of  plant  food.     Approximately  two  thirds 
of  the  nitrogen  of  the  cereal  crops  is  in  the  seeds  and  is 
removed  from  the  farm  when  grains  are  sold.     It  is  also  lost 
from  the  soil  in  the  drainage  water  and  sometimes  by  deni- 
trification.     The  ease  with  which  it  is  lost  from  manure 
has  been  discussed.     It  has  been  said  that  profitable  agri- 
culture depends  upon  an  economical  method  of  conserving 


528  SOILS  AND   FERTILIZERS 

and  renewing  the  nitrogen  supply  of  the  soil.  The  power  of 
legumes  to  fix  the  nitrogen  of  the  air  should  be  utilized  as 
far  as  possible,  and  nitrogen  should  be  ^urchased  only  as  a 
last  resort.  Nitrogen  fertilizers  are  so  expensive  that  the 
matter  of  their  purchase  should  receive  very  careful  con- 
sideration. 

The  principal  sources  of  nitrogen  for  fertilizers  are: 
(1)  the  by-products  of  the  packing  houses  and  rendering 
establishments,  (2)  ammonium  sulphate  from  the  gas  and 
coke  works,  (3)  nitrate  of  soda,  and  (4)  cyanamide. 

620.  Packing  House  By-products.  The  more  common  of 
the  by-products  of  the  rendering,  packing,  and  canning 
establishments  that  handle  meat  and  fish  are  as  follows : 

Dried  blood  containing  from  7  to  10  per  cent  of  nitrogen 
Meat  meal  containing  from  12  to  14  per  cent  of  nitrogen 
Hoof  meal  containing  from  11  to  12  per  cent  of  nitrogen 
Tankage  containing  from  4  to  9  per  cent  of  nitrogen 
Dried  fish  containing  from  8  to  11  per  cent  of  nitrogen 

The  first  three  names  are  self-explanatory.  Tankage 
consists  of  the  refuse  material  that  cannot  be  used  as  human 
food,  and  which  has  been  placed  in  a  tank  and  heated  with 
steam  under  pressure.  The  heating  extracts  the  fat,  which 
is  used  in  soap  making.  Tankage  is,  therefore,  variable  in 
character,  and  in  addition  to  its  nitrogen  contains  from  3 
to  12  per  cent  of  phosphoric  acid  in  the  form  of  bone  meal. 

Most  of  the  fish  fertilizers  are  made  from  menhaden,  a 
fish  that  is  caught  in  large  numbers  along  the  Atlantic  coast. 
The  fish  are  steamed  and  pressed  to  extract  the  oil  and  the 
remaining  pomace  is  dried  and  ground.  This  material 
contains  from  8  to  11  per  cent  of  nitrogen  and  about  3  per 
cent  of  phosphoric  acid.  Some  of  the  fish  fertilizers  consist 


COMMERCIAL  SOURCES  OF  PLANT  FOOD       529 

of  the  residue  of  the  canning  factories,  but  these  are  not  so 
valuable  as  those  derived  from  menhaden. 

621.  Ammonium  sulphate  is  a  by-product  in  the  manu- 
facture of  coal  gas,  animal  charcoal,  and  coke  (93).     It  is 
richest  in  nitrogen  of  all  fertilizing  materials,  containing 
from  20  per  cent  to  23  per  cent.     It  gives  excellent  results 
on  soils  that  contain  plenty  of  calcium  carbonate. 

622.  Nitrate  of  soda  or  Chile  saltpeter  is  a  crystalline 
substance  somewhat  resembling  coarse  salt  in  appearance 
and  is  entirely  soluble  in  water.     It  comes  from  large  deposits 
in  Chile  which  supply  over  one  million  tons  of  nitrate  a  year 
to  be  used  as  a  fertilizer.     Chile  saltpeter  contains  from  15 
per  cent  to  16  per  cent  of  nitrogen  in  a  form  that  is  immedi- 
ately available  to  the  plant,  and  for  this  reason  it  is  the  most 
desirable  nitrogenous  fertilizer  to  use  when  immediate  results 
are  desired.     It  is  not  held  by  the  soil  and  consequently 
should  be  supplied  only  as  it  can  be  used  by  the  crop. 

Calcium  nitrate  as  made  at  the  present  time  in  Norway 
(148)  promises  to  be  an  important  fertilizing  material  of 
the  future. 

623.  Calcium  cyanamide   (CaCN2)   is  a  new  fertilizing 
material.     It  is  produced  by  heating  calcium  carbide  (169) 
to  a  high  temperature  in  a  current  of  nitrogen  until  the 
following  reaction  takes  place : 

CaC2  +  2  N  ->-  CaCN2  +  C. 

Calcium  cyanamide,  called  also  nitro-lime  and  lime 
nitrogen,  is  a  hard  gray-black  substance  resembling  coke 
in  appearance  and  containing  about  20  per  cent  of  nitrogen. 
It  decomposes  in  the  soil  as  follows : 

CaCN2  +  3  H2O  ->•  2  NH3  +  CaCO3. 

EV.    CHEM. 34 


530  SOILS  AND   FERTILIZERS 

Because  calcium  cyanamide  has  an  injurious  effect  upon 
the  germination  of  seeds,  it  should  be  applied  to  the  soil 
some  time  in  advance  of  seeding,  so  as  to  permit  the 
change  to  ammonia  to  be  completed  before  the  seeds 
germinate. 

624.  Low-grade  Nitrogen  Fertilizers.     The  high  price  of 
nitrogen  materials  has  led  to  the  substitution  in  some  cases 
of  inferior  materials  for  the  nitrogen  fertilizers  described 
previously.     Leather  and  horn  meal,  hair  and  wool  wastes, 
shoddy,  dried  peat  and  muck,   and  garbage  tankage  all 
contain  nitrogen,  but  in  a  condition  in  which  it  resists  nitrifi- 
cation and  is  made  available  very  slowly. 

625.  Relative    Availability    of    Nitrogenous    Fertilizers. 
The  percentage  of  nitrogen  present  in  the  different  fertilizing 
materials  does  not  properly  indicate  their  relative  fertilizing 
value.    Mention   has   been   made   repeatedly   of  the   fact 
that  the  plant  can  make  use  of  the  nitrogen  only  when  it  is 
present  in  the  form  of  nitrates.     Nitrate  of  soda  is  the  only 
fertilizer  on  the  list  that  contains  nitrogen  in  the   nitrate 
condition,   and   consequently   is   the   only   one   that   adds 
nitrogen  to  the  soil  in  a  form  which,  without  further  change, 
is  available  to  the  plant.     All  the  other  materials  must  have 
their  nitrogen  converted  into  nitrates  before  it  can  be  used 
by  the  crop.     It  must  be  apparent,  therefore,  that  the  value 
of  a  nitrogenous  fertilizer  depends  upon  both  its  content  of 
nitrogen  and  the  ease  with  which  it  is  nitrified. 

Of  the  list  mentioned,  sulphate  of  ammonia  is  the  most 
easily  converted  into  nitrates,  provided  the  soil  is  abundantly 
supplied  with  lime.  Next  in  order  comes  dried  blood. 

The  nitrogen  in  dried  fish,  tankage,  hoof  meal,  and  bone 
meal  is  readily  changed  by  nitrification  and  ranks  next  to 
blood  meal.  Horn  meal,  on  the  other  hand,  decomposes 


COMMERCIAL  SOURCES  OF  PLANT  FOOD       531 

very  slowly,  and  the  nitrification  of  leather  is  so  slow  as  to 
make  it  practically  worthless  as  a  fertilizer. 

Experiments  up  to  date  indicate  that  if  nitrate  of  soda  is 
rated  at  100  per  cent,  the  availability  of  the  other  materials 
is  as  follows : 

Nitrate  of  soda 100 

Blood 70 

Fish,  hoof  meal          .......     o     ...  65 

Bone  and  tankage 60 

Leather  and  wool  waste 2-10 

626.   Suggestions  for  Using  Nitrogen  Fertilizers.    Two 

or  three  suggestions  for  the  selection  of  nitrogen  fertilizers 
may  be  drawn  from  this  discussion.  For  those  crops  that 
begin  their  growth  early  in  the  spring,  the  best  results  will 
follow  the  use  of  Chile  saltpeter,  as  the  soil  is  likely  to  be 
low  in  nitrates  and  the  process  of  nitrification  is  slow  at 
that  time.  Crops  that  have  very  short  periods  of  growth 
will  respond  best  to  nitrogen  in  nitrates.  On  the  other 
hand,  corn  and  the  other  crops  that  make  their  growth 
after  the  season  is  well  advanced  can  use  the  slower  acting 
fertilizers,  as  can  also  those  crops  that  occupy  the  ground 
permanently.  Some  farmers  prefer  to  use  a  fertilizer  con- 
taining nitrogen  in  three  forms  for  the  crops  that  grow  during 
the  greater  part  of  the  season :  a  little  nitrate  of  soda  for 
immediate  use,  sulphate  of  ammonia  to  supply  the  nitrogen 
a  little  later,  and  tankage  to  carry  the  plant  to  maturity, 
these  materials  being  mixed  and  applied  at  one  time. 

EXERCISES 

Ex.  374.  Explain  why  phosphorus  must  be  used  on  every  farm. 
In  what  ways  is  phosphorus  removed  from  the  farm  ?  Why  is  a  phos- 
phorus fertilizer  needed  even  when  large  quantities  of  feeds  are  pur- 
chased ?  Do  plants  need  a  balanced  ration  ? 


532  SOILS  AND  FERTILIZERS 

Ex.  375.  What  are  the  commercial  sources  of  phosphorus  ?  What 
is  meant  by  raw  bone  meal  ?  By  steamed  bone  meal  ?  Why  is  steamed 
bone  meal  the  more  valuable  ? 

Ex.  376.  What  are  the  sources  of  the  mineral  phosphates?  Why 
are  the  mineral  phosphates  less  available  than  the  bone  phosphates? 
What  is  the  theory  regarding  the  use  of  floats  with  organic  matter  ? 

Ex.  377.  What  is  meant  by  acid  phosphate?  By  what  other 
names  is  it  known?  Write  the  equation  for  the  action  of  sulphuric 
acid  on  mineral  phosphate.  What  may  happen  if  insufficient  sul- 
phuric acid  is  used?  What  is  meant  by  reverted  phosphate?  By 
available  phosphoric  acid?  How  much  available  phosphoric  acid  do 
the  acid  phosphates  contain  ? 

Ex.  378.  What  is  basic  slag?  How  much  phosphoric  acid  does 
it  contain  ?  Is  it  in  an  available  form  ?  Why  is  it  desirable  to  use  a 
phosphate  with  the  stable  manure  ?  Discuss  the  results  obtained  with 
phosphated  manure  at  the  Ohio  Experiment  Station.  How  is  the 
phosphate  best  added  to  the  manure  ? 

Ex.  379.  Why  is  potassium  less  likely  to  be  a  limiting  factor  than 
phosphorus  ?  What  soils  are  most  likely  to  need  potassium  ?  Discuss 
the  European  salts  as  a  source  of  potassium  for  fertilizers.  What  can 
you  say  of  the  value  of  wood  ashes?  Why  should  wood  ashes  be 
protected  from  the  weather  ? 

Ex.  380.  Why  is  nitrogen  sometimes  said  to  be  the  most  important 
element  of  plant  food  ?  What  are  the  principal  sources  of  nitrogen  for 
fertilizers?  Tell  what  you  can  about  the  packing  house  by-products. 
What  is  the  source  of  ammonium  sulphate?  What  is  Chile  saltpeter? 
Calcium  cyanamide  ? 

Ex.  381.  Are  all  nitrogen  materials  equal  in  value?  What  is 
meant  by  the  relative  availability  of  nitrogenous  fertilizers?  What 
is  the  order  of  their  availability?  Give  some  suggestions  for  using 
nitrogen  fertilizers. 


A 

CHAPTER  LX 
MIXED  FERTILIZERS 

627.  Complete  Fertilizers.    By  far  the  larger  part  of  the 
commercial  fertilizers  used  by  farmers  in  this  country  are 
purchased  in  the  form  known  as  complete  fertilizers.     A 
complete  fertilizer,  in  the  sense  in  which  the  word  is  used,  is 
one  that  contains  nitrogen,  phosphoric  acid,  and  potash,  in 
proportions  that  are  supposed  to  be  suited  to  the  require- 
ments of  farm  practice.     Almost  all  these  fertilizers  are 
made  by  mixing  two  or  more  of  the  basic  materials  heretofore 
described,  the  different  ingredients  being  so  combined  as  to 
give  the  desired  percentage  of  nitrogen,  phosphoric  acid,  and 
potash.     In  case  the  basic  materials  alone  yield  a  product 
that  is  richer  in  the  essential  ingredients  than  is  desired  by 
the  manufacturer,  sufficient  gypsum,  dry  earth,  peat,  or  other 
inert  matter  is  added  to  bring  the  percentage  of  these  ingre- 
dients down  to  the  desired  point.     Materials  added  in  this 
way  are  known  as  fillers. 

628.  Home-mixed  Fertilizers.     If  the  farmer  wishes  to 
do  so,  he  may  buy  the  separate  materials  previously  described 
and  mix  them  on  the  farm,  and  in  that  way  save  part  of  the 
expense  of  the  manufacture  of  a  complete  fertilizer.*    There 
are  obvious  advantages  other  than  economy  in  home  mixing 
over  the  purchase  of  mixed  fertilizers.     The  usual  analysis 
of  a  mixed  fertilizer  gives  no  clew  as  to  the  condition  or 
source  of  the  nitrogen,  and  it  is  difficult  to  determine  its 
availability;  while  in  the  homemade  mixture  the  condition 

533 


534 


SOILS  AND   FERTILIZERS 


of  the  nitrogen  can  always  be  known.  Home  mixing  permits 
the  uniting  of  the  different  elements  in  the  proportions  that 
have  been  found  best  to  mejet  the  requirements  of  the  crop 
and  the  soil  on  which  it  is  to  be  raised,  something  that  is 
not  easily  managed  with  factory  mixed  fertilizers.  By 
buying  the  basic  materials  separately  it  is  possible  to  apply 

the  different  elements 
at  different  times,  a 
point  that  is  sometimes 
of  great  advantage  in 
feeding  a  crop,  es- 
pecially if  it  is  one  that 
needs  large  quantities 
of  nitrogen.  In  fact 
the  only  advantage  that 
can  consistently  be 
claimed  for  the  mixed 
goods  is  that  they  are 

FIG.  243.  —  Mixing  fertilizers  on  the  farm.  •,-,        v    ,    M 

more  generally  distrib- 
uted in  the  market  than  the  basic  materials  and  can, 
therefore,  be  more  easily  purchased  in  such  amounts  and  at 
such  times  as  are  convenient. 

A  tight  barn  floor,  a  straight-edged  shovel,  and  a  wire 
screen,  such  as  is  used  for  screening  ashes,  are  the  only 
requisites  for  the  home  mixing  of  fertilizers  (Fig.  243).  The 
mixer  weighs  the  materials  and  spreads  them  upon  the  floor 
in  layers  one  upon  the  other.  Then  beginning  at  one  end 
he  shovels  the  whole  through  the  screen,  repeating  the 
operation  three  or  four  times,  or  until  he  attains  a  fairly 
uniform  mixture. 

629.  Buying  Fertilizers.  In  order  to  protect  the  pur- 
chaser, most  of  the  states  have  passed  laws  compelling  the 


MIXED  FERTILIZERS  535 

manufacturer  to  guarantee  the  amount  of  plant  food  in 
each  brand  of  fertilizer  offered  for  sale.  The  enforcement 
of  these  laws  and  the  chemical  examination  of  the  fertilizers 
to  determine  if  they  agree  with  the  guarantee  are  intrusted 
to  the  experiment  stations  in  some  states,  while  in  others 
they  are  in  the  hands  of  the  State  Department  of  Agriculture. 
The  results  of  the  analyses  are  published  in  bulletins  for 
free  distribution,  and  these  should  be  generally  consulted 
by  farmers  using  fertilizers. 

Fertilizers  should  be  purchased  absolutely  on  the  basis 
of  the  plant  food  that  they  contain,  and  no  attention  should 
be  paid  to  the  name  of  the  brand,  which  usually  bears  no 
relation  to  the  usefulness  of  the  fertilizer.  For  the  sake  of 
simplicity  the  analysis  of  a  fertilizer  is  stated  briefly  in  the 
following  manner:  as  a  3-10-4,  the  figures  meaning  that 
the  fertilizer  contains  3  per  cent  of  nitrogen,  10  per  cent 
of  available  phosphoric  acid,  and  4  per  cent  of  potash,  the 
ingredients  always  being  stated  in  the  same  order. 

630.  Need  of  Knowing  What  Fertilizer  Is  Required.    To 
buy  fertilizers  intelligently  the  farmer  must  first  know  the 
requirements  of  the  crop  and  the  condition  of  the  soil.     A 
soil  that  is  deficient  in  phosphorus,  for  instance,  will  not  be 
much  benefited  by  a  fertilizer  very  low  in  phosphorus,  even 
though  such  a  fertilizer  may  be  valuable  on  other  land.     Un- 
fortunately there  is  no  easy  way  of  determining  accurately 
the  immediate  fertilizer  requirements  of  a  given  soil  for  a 
particular  crop. 

631.  Need  of  Studying  the  Growing  Crop.     In  a  general 
way,  the  crops  themselves  may  give  some  valuable  suggestions. 

(a)  As  a  rule,  lack  of  nitrogen  is  indicated  when  plants 
are  pale  green,  or  when  there  is  small  growth  of  leaf  and 
stalk,  other  conditions  being  favorable. 


536  SOILS  AND   FERTILIZERS 

(b)  A  bright,  deep  green  color  with  a  vigorous  growth  of 
leaf  or  stalk  is,  in  the  case  of  most  crops,  a  sign  that  nitrogen 
is  not  lacking ;  but  such  conditions  do  not  necessarily  indicate 
that  more  nitrogen  could  not  be  used  to  advantage. 

(c)  An  excessive  growth  of  leaf  or  stalk,  accompanied  by 
an  imperfect  bud,  flower,  and  fruit  development  indicates 
too   much   nitrogen   for   the   potash  and  phosphoric  acid 
present. 

(d)  When  such  crops  as  corn,  cabbage,  grass,  and  potatoes 
have  a  luxuriant,  healthful  growth,  an  abundance  of  potash 
in  the  soil  is  indicated.     When  fleshy  fruits  of  fine  flavor 
and  texture  can  be  successfully  grown,  the  same  condition 
is  indicated. 

(e)  When  a  soil  produces  good,  early  maturing  crops  of 
grain,  with  plump  and  heavy  kernels,  phosphoric  acid  will 
not  generally  be  lacking.     A  good  growth  of  straw  with  a 
small  yield  of  grain,  on  the  other  hand,  shows  that  the  soil 
does  not  contain  sufficient  phosphorus  to  balance  the  nitrogen 
and  potash. 

Such  general  indications  may  often  be  helpful,  and  crops 
shojild  be  studied  carefully  with  these  facts  in  mind. 

632.  Field  Experiments.  The  only  reliable  way  of  ascer- 
taining the  proper  fertilizer  to  use  on  a  given  field  is  to 
compel  the  soil  itself  to  answer  the  question.  This  may  be 
done  by  an  easily  conducted  field  experiment.  This  experi- 
ment consists  in  dividing  a  small  portion  of  the  field  into 
small  plots  (Fig.  244)  on  each  of  which  a  different  kind  of 
fertilizer  is  used,  the  yield  being  compared  with  the  yield  of 
check  plots  to  which  no  fertilizing  material  has  been  added. 
Since  the  different  crops  vary  in  their  power  to  extract  plant 
food  from  the  soil,  these  experiments  should  cover  the  entire 
rotation. 


MIXED  FERTILIZERS 


537 


633.  Conducting  the  Experiment.  The  first  important 
consideration  in  an  experiment  of  this  kind  is  the  selection 
of  the  location  for  the  plots.  The  spot  selected  should  rep- 
resent as  nearly  as  possible  the  average  condition  of  the 
entire  field.  The  soil  should  be  uniform  in  quality  over  the 
entire  area  devoted  to  the  experiment,  so  that  one  may  be  sure 
that  any  difference  in  yield  from  the  several  plots  is  not  due 
to  variation  in  the  composition  of  the  soil.  Plots  one  rod 


FlG.  244.  —  View  of  a  field  plot  test  with  fertilizers. 

wide  and  eight  rods  long  will  be  found  a  convenient  size 
for  this  purpose,  but  those  of  any  size  may  be  used.  The 
simplest  experiment  that  will  give  any,  reliable  information 
calls  for  a  row  of  at  least  seven  plots,  with  a  space  of  at  least 
2  feet  between  each  plot.  The  ground  is  first  plowed  and 
harrowed  and  then  the  plots  are  measured  out,  each  corner 
being  marked  by  a  stake  driven  well  into  the  ground.  The 
fertilizers  for  each  division  are  mixed  and  applied  by  hand, 
care  being  used  not  to  scatter  the  material  beyond  the  plot 
for  which  it  is  intended.  The  diagram  (Fig.  245)  shows  the 


538  SOILS  AND  FERTILIZERS 

arrangement  of  the  plots  and  the  kind  and  quantity  of  fer- 
tilizing material  to  be  used  on  each. 


1 

No  Fertilizer 

2 

15  Ib.  Nitrate  of  Soda 
15  Ib.  Sulphate  of  Potash 
30  Ib.  Acid  Phosphate 

3 

30  Ib.  Acid  Phosphate 
15  Ib.  Sulphate  of  Potash 

4 

No  Fertilizer 

5 

15  Ib.  Nitrate  of  Soda 
15  Ib.  Sulphate  of  Potash 

C 

15  Ib.  Nitrate  of  Soda 
30  Ib.  Acid  Phosphate 

7 

No  Fertilizer 

FIG.  245.  —  Arrangement  of  plots  and  quantity  of  fertilizer  used  in  conducting 
a  field  experiment. 

The  plots  may  be  seeded  separately,  but  it  saves  labor 
and  gives  practically  as  good  results  if  they  are  planted  with 
the  rest  of  the  field.  In  any  case  the  seeder  must  be  run 
lengthwise  of  the  plots  so  as  to  avoid  dragging  any  of  the 
fertilizer  from  one  plot  to  another. 

634.  Harvesting  the  Crop.  The  area  devoted  to  the 
experiment  should  receive  exactly  the  same  treatment 
during  the  growing  season  as  the  rest  of  the  field,  except  that 


MIXED  FERTILIZERS  539 

in  no  case  is  cross  cultivation  of  the  plots  allowable.  If  the 
crop  is  one  that  is  planted  in  rows  and  intertilled,  it  will 
be  best  to  harvest  the  same  number  of  rows  from  the  center 
of  each  plot,  discarding  the  outer  rows.  In  the  case  of  small 
grains,  a  cord  is  stretched  from  stake  to  stake  to  outline 
the  plots  and  the  grain  is  first  removed  from  the  intervening 
spaces.  This  leaves  each  plot  standing  out  so  distinctly 
that  it  can  be  readily  observed  and  the  crop  can  easily  be 
harvested.  The  weight  of  both  grain  and  straw  from  each 
plot  should  be  determined. 

635.  Interpreting  the  Results.  The  yield  from  each  of  the 
check  plots  should  be  practically  the  same.  If  this  is  the 
case,  it  shows  that  the  soil  in  the  area  devoted  to  the  experi- 
ment is  uniform  in  character.  A  little  thought  will  show 
how  to  decide  from  the  experimental  data  what  elements  of 
fertility  give  satisfactory  results  with  the  crop  and  soil 
under  investigation.  If  the  yield  on  all  the  plots  is  about  the 
same,  for  instance,  it  will  be  evident  that  no  beneficial 
results  can  be  expected  on  that  soil  from  the  use  of  commercial 
fertilizers.  If  plot  number  2  gives  higher  results  than  any  of 
the  others,  it  is  to  be  concluded  that  nitrogen,  phosphoric 
acid,  and  potash  are  all  required.  If  plots  2,  3,  and  6 
give  larger  yields  than  the  checks,  and  5  does  not,  the  indi- 
cation is  that  phosphoric  acid  alone  is  necessary.  An 
increased  yield  on  2,  3,  and  5  but  not  on.  6  indicates  need  of 
potash.  A  larger  crop  on  2,  5,  and  6  but  not  on  3  shows  need 
of  nitrogen.  A  large  increase  in  yield  over  the  checks  on  2 
and  6  and  a  smaller  increase  on  3.  and  5  suggest  that  both 
nitrogen  and  phosphoric  acid  are  beneficial  but  potash  is 
not ;  and  so  on. 

Experiments  similar  to  these  are  being  conducted  by  many 
of  the  state  experiment  stations  on  the  different  types  of  soil 


540  SOILS  AND  FERTILIZERS 

found  in  the  several  states,  so  as  to  assist  the  farmer  in 
determining  what  kinds  of  fertilizers  are  needed  for  his 
particular  farm. 

636.  Commercial  Fertilizers  Not  All-sufficient.  Absolute 
dependence  should  not  be  placed  on  commercial  fertilizers 
alone  to  maintain  the  fertility  of  the  land.  Commercial 
fertilizers  add  little  or  no  humus  to  the  soil,  and  to  obtain 
the  best  results  it  is  absolutely  necessary  to  provide  humus, 
either  by  plowing  under  green  crops  or  by  the  use  of  barnyard 
manure.  Numerous  experiments  have  shown  that  com- 
mercial fertilizers  give  much  better  returns  when  used  in 
connection  with  barnyard  manure  than  if  used  alone,  and 
they  are  coming  into  use  in  this  manner  more  and  more  as 
the  subject  is  more  thoroughly  investigated. 

It  may  be  said  in  this  connection  that  commercial  fertilizers 
are  not  merely  stimulants,  as  is  frequently  imagined,  but 
that  they  actually  supply  plant  food.  If  rationally  used, 
they  will  leave  the  soil  more  fertile  than  before  their  use, 
instead  of  decreasing  its  fertility,  as  would  happen  if  a  mere 
stimulant  were  used.  Commercial  fertilizers  have  an  im- 
portant place  in  the  rural  economy ;  but  they  should  not  be 
used  to  do  the  work  that  can  better  be  accomplished  by 
proper  husbanding  of  home  rssources. 

EXERCISES 

Ex.  382.  What  is  meant  by  a  complete  fertilizer?  How  are 
complete  fertilizers  made?  What  is  meant  by  a  filler?  Find  the 
brand  names  and  the  analyses  of  the  fertilizers  used  by  the  farmers 
in  your  locality. 

Ex.  383.  What  are  the  advantages  of  the  home  mixing  of  ferti- 
lizers? How  should  you  proceed  to  make  a  home-mixed  fertilizer? 
How  could  you  make  a  3-10-4  fertilizer  from  the  following  materials : 
Nitrate  of  soda  containing  16  %  nitrogen,  acid  phosphate  containing 


MIXED  FERTILIZERS  541 

16  %  phosphoric  acid,  and  muriate  of  potash  containing  50  %  potash? 
How  much  filler  would  be  required  ? 

Ex.  384.  What  does  a  farmer  need  to  know  before  buying  a  fer- 
tilizer? Upon  what  basis  should  the  fertilizer  be  purchased?  How 
much  attention  should  be  paid  to  the  name  of  the  fertilizer?  Explain 
how  the  crop  may  indicate  what  fertilizer  is  needed. 

Ex.  385.  Describe  a  field  experiment  to  determine  the  fertilizer 
requirements  of  a  soil.  The  following  results  were  obtained  in  an  actual 
experiment  similar  to  the  one  described :  plots  1,  4,  and  7  yielded  10 
bushels  of  wheat  to  the  acre.  Plots  2,  3,  5,  and  6  yielded  26,  19,  13, 
and  23  bushels  in  the  order  named.  Were  all  three  elements  of  fer- 
tility needed?  Can  you  tell  which  element  was  most  needed?  Does 
the  experiment  show  whether  there  was  more  need  of  potash  or  nitrogen  ? 

Ex.  386.  In  another  actual  experiment  plots  1,  4,  and  7  produced 
only  6  bushels  of  wheat  to  the  acre.  Plots  2,  3,  5,  and  6  produced  19, 
16,  9,  and  19  bushels  in  the  order  named.  What  elements  are  needed 
in  this  soil  ?  Which  element  appears  to  be  most  needed  ? 


CHAPTER  LXI 
TYPES  OF  FARMING  AND   FERTILITY 

637.  Some  Fertilizer  Always  Needed.     While  soils  vary 
greatly  in  their  original  fertility,  so  that  it  is  customary  to 
speak  of  rich  and  poor  soils,  it  is  also  true  that  none  of  them 
can  long  produce  crops  without  the  addition  of  some  kind  of 
fertilizing   material.     Any   system   of   farming   that    is   to 
succeed  through  a  long  period  of  years  must  provide  some 
method  of  replacing  practically  all  the  plant  food  removed, 
no  matter  how  rich  the  soil  was  in  its  virgin  condition. 

Each  farm  is  in  a  measure  a  special  study ;  but  the  work 
done  by  the  various  agricultural  experiment  stations  makes 
it  possible  to  formulate  a  few  important  generalizations. 
If  the  farms  are  properly  drained,  if  tillage  is  thorough  and 
rational,  if  limestone  has  been  added  where  necessary,  and 
if  crops  are  rotated,  the  system  of  fertilization  necessary  for 
best  results  in  the  various  types  of  farming  would  be  about 
as  outlined  in  the  following  sections. 

638.  All   Crops   Sold.     Where   all   the   crops,    including 
straw  and  hay,  are  sold  from  the  farm,  the  fertility  of  the 
soil  is  quickly  exhausted  unless  fertilizers  are  freely  used. 
In  this    case   dependence   must  be  placed  upon  fertilizers 
that  supply  nitrogen,  phosphorus,   and  potassium,  and  a 
sufficient  quantity  -must  be  used  to  replace  practically  all 
the  plant  food  removed  from  the  soil.     Some  difference  of 
opinion  exists  as  to  whether  the  fertilizer  should  be  used 
wholly  on  the  cereals,  or  on  the  hay  crop   as    well.     An 

542 


TYPES  OF  FARMING  AND   FERTILITY  543 

experiment  on  this  type  of  farming  which  has  been  running 
for  twenty  years  at  the  Ohio  Experiment  Station,  an 
experiment  in  which  the  rotation  followed  was  corn,  oats, 
wheat,  clover,  and  timothy  and  in  which  the  fertilizer 
was  used  on  the  corn,  oats,  and  wheat,  gave  an  annual 
profit  for  the  use  of  the  fertilizer  of  $3.53  an  acre  over 
and  above  the  cost  of  the  application.  The  total  fertilizing 
materials  used  on  the  three  grain  crops  during  each  rotation 
consisted  of  480  pounds  of  nitrate  of  soda,  320  pounds  of 
acid  phosphate,  and  260  pounds  of  muriate  of  potash.  Later 
experiments  indicate  that  less  nitrogen  and  potassium  and 
more  phosphorus  would  have  given  greater  profit.  Under 
the  best  of  circumstances,  however,  the  total  possible  profit 
from  this  type  of  farming  is  comparatively  small. 

639.  Grains  Only  Sold.     In  the  end  it  will  probably  be 
found  more  profitable  to  sell  the  grain  only  and  return  the 
straw  and  clover  for  their  manurial  effects.     A  four-year 
rotation  of  corn,  oats,  wheat,  and  clover  will  serve  as  an 
example.     In  this  type  of  farming  the  only  loss  is  in  phos- 
phorus,   provided   the    clover,    straw,    and    cornstalks   are 
plowed  under ;  for  in  this  case  the  fixation  of  nitrogen  by  the 
clover  should  make  up  for  that  sold  in  the  grain.     The  only 
commercial  fertilizer  that  need  be  purchased,  therefore,  is 
acid  phosphate  or  some  other  carrier  of  phosphoric  acid. 
This  type  of  farming  is  being  recommended  for  the  great 
grain-growing  and  cotton-growing  sections. 

640.  Dairy   Farming.    The   type   of   farming   in   which 
fertility  is  most  easily  maintained  is  the  one  devoted  wholly 
to  dairying,  in  which  only  such  crops  are  raised  as  can  be 
fed  on  the  farm.     The  dairy  farmer  finds  it  profitable  in 
milk   production   to   purchase   quantities   of   concentrated 
feeds,  and  thereby  bring  plant  food  to  the  farm.    To  reen- 


544  SOILS  AND  FERTILIZERS 

force  the  manure  he  should  purchase  acid  phosphate  which 
is  preferably  used  in  the  stable  at  the  rate  of  one  pound  a 
day  for  each  animal  (612).  Under  these  conditions  the  farm 
will  increase  in  fertility  if  the  manure  is  properly  preserved. 
One  run-down  farm  that  was  producing  only  30  bushels  of 
corn  to  the  acre  was  made  to  yield  85  bushels  to  the  acre 
within  eight  years  by  this  method  of  farming. 

641.  Fat  Stock  Farming.     The  same  general  principles 
apply  in  this  case  as  in  dairy  farming;   but  as  the  stock 
feeder  usually  does  not  buy  as  much  feeding  stuffs  as  the 
dairyman,  the  farm  is  not  so  easily  maintained  in  a  high  state 
of  fertility. 

642.  Mixed  Farming.     Most  of  the  farms  of  this  country 
are  managed  by  the  system  known  as  mixed  farming,  in 
which  some  of  the  crops  are  sold  directly  and  the  rest  fed 
to  the  animals  and  marketed  as  animal  products.     Under 
this  system  all  the  manure  should  be  carefully  saved,  ree'n- 
forced  with  some  phosphate  material,  and  applied  to  the 
land  that  is  to  be  plowed  for  corn,  provided  that  crop  ap- 
pears in  the  rotation.     Additional  phosphorus  should  be 
used  on  the  small  grains,  especially  upon  wheat  if  grown, 
since  they  respond  readily  to  such  treatment.     In  case  the 
land  is  not  in  a  high  state  of  fertility  it  may  also  be  found 
profitable  to  use  small  quantities  of  nitrogen  and  potassium 
on  the  wheat.    At  the  Ohio  Experiment  Station  there  is  a 
tract  of  forty  acres  which  is  being  managed  according  to 
this  system.     The  rotation  is  corn,  oats,  wheat,  and  clover, 
with  ten  tons  to  the  acre  of  phosphated  .manure  applied  to 
the  corn,  and  chemical  fertilizers  to  the  wheat.     In  the  12 
years  that  this  plan  has  been  in  operation  the  yields  of  the 
several  crops  have  increased  as  follows :   corn  from  34  to  78 
bushels,  oats  from  30  to  60  bushels,  wheat  from  15  to  34 


TYPES  OF  FARMING  AND  FERTILITY  545 

bushels,  and  clover  hay  from  2000  to  6400  pounds  to  the 
acre,  with  indications  that  the  maximum  yields  have  not 
yet  been  reached. 

A  great  many  of  the  farms  devoted  to  mixed  farming  do 
not  produce  sufficient  manure  to  make  possible  the  applica- 
tion of  ten  tons  to  each  acre  once  in  four  years.  In  such 
cases  it  will  probably  be  necessary  to  resort  to  the  occasional 
use  of  some  form  of  green  manuring  if  the  yields  are  to  be 
maintained  at  a  high  level. 

643.  Special  Crops.    There  are  certain  so-called  special 
crops  on  which  it  has  long  been  customary  to  use  large 
quantities  of  commercial  fertilizers.     These  crops,  among 
which  are  tobacco,  sugar  beets,  potatoes,  onions,  cotton,  and 
celery,  bring  relatively  high  prices  per  acre,  and  consequently 
are  more  likely  to  give  profitable  returns  for  heavy  fertili- 
zation than  are  the  ordinary  farm  crops.     It  is  quite  a  com- 
mon practice  to  use  from  1000  to  2000  pounds  to  the  acre 
of  a  high-grade  chemical  mixture  containing  all  the  elements 
of  fertility  upon  these  special  crops.     While  this  practice 
gives  good  profits  under  favorable  conditions,  there  is  need 
of  much  more  experimental  work  with  these  plants  before 
it  can  safely  be  assumed  that  this  is  the  most  economical 
and  profitable  scheme  of  fertilization  even  for  these  high- 
priced  crops.     Onions  and  celery,  it  should  be  noted,  are 
frequently  grown  on  a  muck  or  peaty,  soil,  in  which  case 
the  need  of  potassium  in  the  fertilizer  is  evident. 

644.  Market  gardening  may  be  said  to  be  one  of  the  most 
intensive  forms  of  farming.     The  areas  farmed  are  small, 
and  a  large  amount  of  hand  labor  is  involved.    The  money 
returns  for  each  acre  are  relatively  large,  and  the  gardener  is 
justified  in  making  large  expenditures  to  maintain  fertility. 
The  mechanical  condition  of  the  soil  is  of  prime  importance, 

EV.  CHEM.  —  35 


546  SOILS  AND  FERTILIZERS 

especially  in  the  production  of  the  root  crops,  such  as  radishes, 
carrots,  parsnips,  and  beets.  The  best  practice  is  to  use 
composted  manure  in  large  quantities,  supplementing  it 
with  green  manures,  if  the  supply  of  stable  manure  is  not 
sufficient  to  maintain  a  high  percentage  of  organic  matter 
in  the  soil.  The  Chinese,  who  are  excellent  gardeners,  grow 
clovers  and  other  legumes  which  they  compost  with  earth 
and  use  in  lieu  of  composted  stable  manure.  Since  it  is 
becoming  increasingly  difficult  for  most  gardeners  to  secure 
stable  manure,  this  practice  of  the  Chinese  gardener  may 
be  found  to  be  useful  in  this  country  under  some  conditions. 
Phosphoric  acid  and  potash  fertilizers  should  be  used  in 
abundance,  preferably  in  the  compost,  since  they  are  re- 
tained by  the  soil,  and  extra  nitrogen  should  be  supplied  in 
the  form  of  nitrate  of  soda  as  needed  by  the  crops.  Nitrate 
of  soda  is  especially  valuable  for  the  leafy  crops  that  make 
their  growth  in  the  early  spring,  such  as  spinach,  lettuce,  early 
cabbage  and  cauliflower,  asparagus,  and  rhubarb.  The  prices 
obtained  from  these  crops  depend  largely  upon  their  earliness, 
and  nitrate  of  soda  forces  them  into  rapid  growth.  Peter 
Henderson  tells  of  one  case  in  which  an  acre  of  very  early 
cauliflower  sold  for  $1000,  while  an  adjoining  acre  which, 
because  of  improper  fertilization,  was  two  weeks  later  in 
reaching  the  market  brought  only  $200. 

645.  Orcharding.  In  too  many  cases  the  orchard  receives 
no  fertilizer  of  any  kind,  and  yet  on  many  soils  the  orchard 
fruits  give  handsome  returns  for  fertilization.  Either  manure, 
commercial  fertilizers,  or  both  may  be  used  with  good  results. 
Cover  crops,  which  can  be  plowed  under  or  used  around  the 
trees  as  a  mulch,  are  of  assistance  in  fertilizing  an  orchard. 
The  frontispiece  shows  how  readily  apple  trees  respond  to 
fertilizers  on  some  soils. 


TYPES   OF  FARMING  AND  FERTILITY  547 

646.  Permanent  Pastures.  The  most  neglected  part  of 
the  average  American  farm  is  the  area  devoted  to  the  per- 
manent pasture.  It  seems  to  be  assumed  that  the  soil 
can  produce  pasture  grasses  indefinitely  without  fertiliza- 
tion, and  these  areas  in  the  older  parts  of  the  country  show 
the  effect  of  such  neglect.  The  pastures  should  be  as  care- 
fully fertilized  as  any  part  of  the  farm.  The  best  fertilizer 
to  use  when  it  is  available  is  phosphated  stable  manure 
applied  with  the  manure  spreader.  Permanent  pastures 
have  a  tendency  to  become  acid  and,  therefore,  should 
receive  occasional  applications  of  limestone.  When  stable 
manure  is  not  available  chemical  fertilizers  may  be  used  to 
advantage.  Acid  phosphate  or  bone  meal  should  be  used 
freely  with  a  moderate  amount  of  potash  salts.  The  addition 
of  nitrate  of  soda  will  encourage  the  growth  of  the  true 
grasses,  such  as  blue  grass,  but  if  it  is  desired  to  promote 
the  growth  of  the  clovers  rather  than  the  grasses  the  nitrate 
should  be  omitted.  The  pastures  should  be  dragged  from 
time  to  time  to  distribute  the  droppings  of  the  animals,  and 
they  are  also  benefited  by  an  occasional  clipping  with  the 
mowing  machine. 

EXERCISES 

Ex.  387.  Will  any  soil  produce  crops  indefinitely  without  fertiliza- 
tion ?  Name  four  things  that  are  fundamental  to  soil  fertility.  How 
can  fertility  be  maintained  if  all  the  crops'  are  sold  from  the  farm? 
What  can  you  say  of  the  probable  profit  of  this  type  of  farming  if  long 
continued?  Could  the  fertility  be  more  readily  maintained  if  only 
the  grains  were  sold?  What  fertilizer  would  need  to  be  supplied  in 
that  case?  Explain.  Under  what  circumstances  is  this  type  of  farm- 
ing recommended  ? 

Ex.  388.  How  may  the  fertility  be  maintained  on  dairy  farms? 
Why  is  it  desirable  to  add  a  phosphate  to  the  manure  even  when  con- 
centrates are  purchased?  Are  there  any  dairy  or  stock  farms  near 


548  SOILS  AND  FERTILIZERS 

the  school ?  Is  the  manure  properly  cared  for  on  these  farms?  Ascer- 
tain whether  any  of  the  farmers  use  phosphate  with  the  manure. 

Ex.  389.  What  is  meant  by  mixed  farming?  If  a  farm  used  a 
rotation  of  corn,  oats,  wheat,  and  clover,  and  all  the  wheat  and  half 
the  corn  and  oats  were  sold,  and  the  other  materials  were  used  on  the 
farm,  what  plan  of  fertilization  should  you  recommend  for  the  farm  ? 
Explain  why.  When  is  green  manuring  advisable  in  mixed  farming  ? 

Ex.  390.  Tell  what  you  can  about  fertilizers  for  special  crops. 
If  any  of  the  special  crops  named  in  the  text  are  grown  in  your  neigh- 
borhood report  on  the  fertilizer  used  on  them.  Why  is  the  mechanical 
condition  of  the  soil  of  prime  importance  in  market  gardening  ?  What 
is  the  best  way  to  improve  the  mechanical  condition  of  the  soil  ?  Why 
is  nitrate  of  soda  especially  valuable  to  the  market  gardener  ?  In  case 
stable  manure  cannot  be  procured  how  may  the  amount  of  compost 
be  increased? 

Ex.  391.  Does  it  pay  to  fertilize  the  orchard  ?  What  method  may 
be  used  ?  What  is  meant  by  a  cover  crop  ?  Are  there  any  orchards 
in  your  vicinity  in  which  cover  crops  are  used  ?  What  kinds  ?  What 
can  you  say  about  the  need  of  fertilizing  the  permanent  pastures? 
What  is  the  best  fertilizer  for  pastures?  What  chemicals  should  you 
recommend  if  blue  grass  was  especially  desired?  What  other  treat- 
ment should  you  suggest  for  the  pastures? 


APPENDIX 


(a)   LIST  OF   CHEMICALS    NEEDED   FOR  A  CLASS  OP 
TWELVE 

These  chemicals  may  be  of  the  grade  known  as  "Pure"   and  need 
not  be  of  the  more  expensive  C.  P.  grade. 


2  Ib.  Acid,  acetic 

4  oz.  Acid,  arsenious 

2  oz.  Acid,  benzoic 

4  oz.  Acid,  boric 

4  oz.  Acid,  carbolic 

4  oz.  Acid,  citric,  crystals 

6  Ib.  Acid,  hydrochloric 

2  oz.  Acid,  lactic 

6  Ib.  Acid,  nitric 

4  oz.  Acid,  oxalic,  crystals 

4  oz.  Acid,  phosphoric 

1  oz.  Acid,  salicylic 

18  Ib.  Acid,  sulphuric,  commercial 
9  Ib.  Acid,  sulphuric,  pure 

2  oz.  Acid,  tannic 

4  oz.  Acid,  tartaric,  crystals 

1  gal.  Alcohol,  denatured 

1  pt.  Alcohol,  grain 

1  qt.  Alcohol,  wood 

8  oz.  Alum,  ammonium 

8  oz.  Alum,  chrome 

8  oz.  Alum,  ferric 

8  oz.  Alum,  potassium 

1  Ib.  Aluminum  sulphate 

1  Ib.  Ammonium  carbonate 

1  Ib.  Ammonium  chloride 

8  Ib.  Ammonium  hydroxide 

2  oz.  Ammonium  molybdate 
1  Ib.  Ammonium  nitrate 

1  Ib.  Ammonium  sulphate 
8  oz.  Barium  chloride 
8  oz.  Barium  hydroxide 
8  oz.  Barium  nitrate 
1  can  Bleaching  powder 


1  Ib.  Calcium  carbide 
8  oz.  Calcium   carbonate,    precipi- 
tated 

1  Ib.  Calcium  chloride 
1  Ib.  Calcium  fluoride 
1  oz.  Calcium  metal 
1  Ib.  Calcium  phosphate 

1  Ib.  Calcium  sulphate 

2  Ib.  Carbon  bisulphide 

1  Ib.  Carbon  tetrachloride 
1  Ib.  Carborundum 
1  Ib.  Charcoal,  animal 
1  Ib.  Charcoal,  wood 
8  oz.  Chloroform 

1  oz.  Cobalt  nitrate 

2  oz.  Cochineal  bugs 
4  oz.  Collodion 

4  oz.  Copper  oxide,  coarse 

5  Ib.  Copper  sulphate 
8  oz.  Copper  turnings 

4  oz.  Cresol 

1  Ib.  Dextrose,  lump 
1  Ib.  Ether 

5  Ib.  Formaldehyde 
8  oz.  Gfall  nuts 

1  Ib.  Glycerin 

4  oz.  Gum  arabic 
4  oz.  Gum  damar 
4  oz.  Hydrogen  peroxide 

2  oz.  Iodine 

4  oz.  Iron  ammonium  citrate 
1  Ib.  Iron  pyrites 
1  Ib.  Iron  sulphate 
1  Ib.  Iron  sulphide 


549 


550 


APPENDIX 


(a)   LIST  OF  CHEMICALS   NEEDED  (Continued) 


1  Ib.  Kaolin 

4  oz.  Lampblack 

1  Ib.  Lead  acetate 
1  Ib.  Lead  arsenate 
1  Ib.  Lead  metal 
1  Ib.  Lead  oxide,  red 

1  Ib.  Lead  oxide,  yellow 

5  vials  Litmus  paper,  blue 
5  vials  Litmus  paper,  red 
4  oz.  Litmus  solution 

4  oz.  Logwood  extract 
4  oz.  Magnesium  chloride 

2  oz.  Magnesium  powder 
2  oz.  Magnesium  ribbon 

8  oz.  Magnesium  sulphate 

1  oz.  Maltose 

2  Ib.  Manganese  dioxide 
2  Ib.  Mercury 

2  oz.  Mercury  bichloride 
1  Ib.  Naphthalene 
1  Ib.  Oil,  cottonseed 
1  Ib.  Oil,  linseed,  boiled 
1  Ib.  Oil,  linseed,  raw 
8'  oz.  Oil,  olive 
1  oz.  Oil,  wintergreen 

1  oz.  Pancreatin 

2  Ib.  Paraffin 

8  oz.  Paris  green 
2  oz.  Pepsin,  scale 
1  Ib.  Petrolatum 

1  oz.  Phenolphthalein 

2  oz.  Phosphorus,  red 

2  oz.  Phosphorus,  yellow 

1  oz.  5%  sol.  Platinum  chloride 

1  Ib.  Potassium  bichromate 

1  Ib.  Potassium  bitartrate 

2  oz.  Potassium  bromide 

1  Ib.  Potassium  carbonate 

2  Ib.  Potassium  chlorate 
8  oz.  Potassium  chloride 


2  oz.  Potassium  cyanide 

4  oz.  Potassium  ferricyanide 

8  oz.  Potassium  hydroxide,  sticks 

2  oz.  Potassium  iodide 

1  oz.  Potassium  metal 

1  Ib.  Potassium  nitrate 

8  oz.  Potassium  permanganate 

1  Ib.  Potassium  sulphate 

2  Ib.  Rochelle  salts 

1  Ib.  Rosin,  common 
4  oz.  Shellac 

2  oz.  Silver  nitrate 
1  Ib.  Soda  lime 

1  Ib.  Sodium  acetate 
4  oz.  Sodium  arsenite 

2  oz.  Sodium  benzoate 

1  Ib.  Sodium  bicarbonate 
1  Ib.  Sodium  borate 

1  Ib.  Sodium  carbonate 

4  Ib.  Sodium  hydroxide,  sticks 

2  Ib.  Sodium  hyposulphite 
2  oz.  Sodium  metal 

2  Ib.  Sodium  nitrate 

4  oz.  Sodium  nitrite 

8  oz.  Sodium  peroxide 
1  Ib.  Sodium  phosphate 
1  gal.  Sodium  silicate 
1  Ib.  Sodium  sulphate 

1  Ib.  Sodium  sulphite 

2  Ib.  Sulphur,  flowers  of 

8  oz.  Sulphur,  precipitated 
2  Ib.  Sulphur,  roll 
1  Ib.  Turpentine 
1  oz.  Vermilion 

5  Ib.  Zinc,  mossy 
8  oz.  Zinc  chloride 
1  Ib.  Zinc  dust 

1  Ib.  Zinc  oxide 
1  Ib.  Zinc  sulphide 


APPENDIX 


551 


(6)    SUBSTANCES   WHICH   MAY    BE    OBTAINED    LOCALLY 
AS   REQUIRED 


Absorbent  cotton 

"Ammo"  solid  ammonia 

Ammonia,  household 

Candles 

Chloride  of  lime 

Coal,  hard 

Coal,  soft 

Coke 

Cream  of  tartar 

Dry  cells 


Fertilizing  materials 
Gasoline 
Gelatin,  Jello 
Grain  products : 

Barley 

Corn  meal 

Dextrin 

Flaxseed 

Malt 

Oats 

Various  starches 

Wheat  flour 
Graphite 

Insect  powders  —  pyrethrum 
Insecticides,  nicotine 
Iron,  cast 
Iron,  wrought 
Karo  sirup 
Kerosene 
Lime 

Limestone  and  marble 
Milk  products : 

Butter 

Buttermilk 


Condensed  milk 

Powdered  milk 

Renovated  butter 

Skim  milk 

Whole  milk 
Miscellaneous  fats : 

Cocoanut  oil 

Cottolene 

Crisco 

Lard 

Oleomargarine 

Tallow 

Paints  and  varnishes 
Paraform  or  formacone 
Petroleum,  crude 
Picture  frame  wire 
Plaster  of  Paris 
Portland  cement 
Raisins 

Rennet  extract 
Salt 

Sapolio  and  scouring  soaps 
Soap  powders 
Soaps,  various 
Steel 
Sugar 
Textiles : 

Cotton  cloth 

Linen  cloth 

Mixed  cotton  and  wool 

Silk  cloth 

Woolen  cloth 
Vinegars 
Wood  ashes 
Yeast,  compressed 


552 


APPENDIX 


(c)    APPARATUS   FOR   GENERAL  USE 

Figure  numbers  refer  to  illustrations  of  the  apparatus  in  the  text. 
Homemade  apparatus  may  be  prepared  as  substitutes  for  many  of 
the  articles  in  lists  c  and  d. 


Balance  —  Capacity  2  pounds  sen- 
sitive to  0.1  gram  (Fig.  59) 

Apparatus  for  electrolytic  dissocia- 
tion of  water  (Fig.  49) 

Eudiometer  (Fig.  54) 

Air  pump  (Fig.  31) 

Microscope 

Water  oven  (Fig.  142) 

Babcock  testing  outfit  with  glass- 
ware for  milk,  skim  milk,  and 
cream  (Figs.  164-170) 

Quevenne  lactometer  (Fig.  171) 

Truog  soil  tester  (Fig.  226) 

Graham-McCall  drainage  appara- 
tus (Fig.  206) 

Soil  auger  (Fig.  193) 


Gasoline  blast  torch  (Fig.  5) 

Magnet 

Set  of  cork  borers  (Fig.  13) 

2  matched  F.  thermometers  (Fig. 

40) 

1  centigrade  thermometer  (Fig.  3C) 
Separatory  funnel  (50  cc.)  (Fig.  84) 
Small  piece  platinum  wire 
Large  glass  tubes  or  lamp  chimneys 

(Fig.  204) 
One  quart  sprayer  for  oat  smut 

exercise 

Tall  glass  cylinder 
Small  combustion  burner  (Fig.  44) 
Mortar  and  pestle 


(d)    APPARATUS    REQUIRED   FOR   EACH    STUDENT    WHO 
IS   TO   PERFORM    THE   EXPERIMENTS 


10  ft.  small  glass  tubing,  5  mm. 
Bunsen    burner    or    alcohol    lamp 

(Figs.  1,  2) 

Corks,  common  and  2-hole  rubber 
6  test  tubes,  common 
Test  tube,  hard  glass 
Test  tube  brush 

Evaporating  dish,  2  in.  (Fig.  27) 
Florence  flask,  500  cc.  (Fig.  25) 
Florence  flask,  1000  cc.  (Fig.  12) 
Condenser  (Fig.  28) 
Bottles  of  various  sizes 
Watch  glass,  2|  in.  (Fig.  37) 

1  ft.  hard  glass  tubing,  1|  cm. 

2  beakers    (500   cc.    and  250   cc.) 

(Fig.  15) 


Pinchcock 

CaCl2  drying  tube  (Fig.  48) 

Thistle  tube  (Fig.  46) 

Funnel,  2£  in.  (Fig.  20) 

Crucible,  porcelain  (Fig.  83) 

Graduated  glass  cylinder,  100  cc. 

(Fig.  172) 
Triangular  file 
Rat-tail  file 
Blow  pipe  (Fig.  125) 
Ring  stand  with  rings  and  clamps 

(Fig.  20) 
Wire  gauze 

Glass  plates,  3  in.  x  3  in. 
Asbestos  paper 


INDEX 


Numbers  immediately  following  titles  refer  to  pages  of  the  text.     Those 
following  the  abbreviation  "Ex."  refer  to  numbers  of  the  experiments. 


Acetic  acid,  256,  Ex.  164 

from  wood,  257 
Acetylene,  247,  Ex.  158 
Acid  phosphate,  190,  Ex.  113 
Acid  resistant  plants,  482 
Acids,  154,  156,  157 
Affinity,  chemical,  101 
Air,  70 

a  mechanical  mixture,  71 

contains  carbon  dioxide,  73,  Ex.  44 

contains  warter  vapor,  72,  Ex.  43 

liquid,  75 

Albumin,  283,  Ex.  198,  Ex.  199 
Albuminoids,  284 
Alcoholic  beverages,  251 
Alcohols,  250-254 

are  bases,  252 

denatured,  252 

grain,  250 

wood,  250 
Alkali,  156,  Ex.  94 

in  cleaning,  407 
Alkaloids,  286 
Allotropy,  81 
Alloys,  231,  Ex.  145 
Aluminum,  214 

occurrence  of,  215 

preparation  of,  215 

test  for,  219 

Aluminum  sulphate,  216 
Alums,  216,  Ex.  131 
Amines,  285 
Ammonia,  171,  Ex.  103 

composition  of,  173 

from  organic  matter,  172,  Ex.  104 

in  ice  making,  177 

manufacture  of,  173 

occurrence  of,  178,  Ex.  110 

test  for,  179 


Ammonia  water,  171 

neutralizes  acids,  174,  Ex.  106 
Ammonium  carbonate,  177 
Ammonium  chloride,  176 
Ammonium  hydroxide,  174 
•Ammonium  nitrate,  176 
Ammonium  sulphate,  176 
Amylopsin,  320 
Analysis,  56 
Anhydride,  159 
Antiseptics,  389 
Aqua  ammonia,  171 
Aqua  fortis,  165 
Aquaregia,  165 
Arsenates,  191 
Arsenic,  190 
Arsenites,  191,  Ex.  114 
Ash,  in  plants,  290 
Atomic  theory,  91,  92 

applied,  93 
Atomic  weights,  93 

Babcock  formula,  372 
Babcock  test,  364 

composite  test,  370 

for  buttermilk,  368 

for  cheese,  370 

for  cream,  369 

for  milk,  365 

for  skim  milk,  368 
Bacterial  diseases  of  plants,  418 
Baking  powders,  380,  Ex.  266 

homemade,  381,  Ex.  268 
Baking  soda,  150,  380 
Balanced  rations,  331 

calculating,  334 

for  human  beings,  342 
Bases,  154,  156,  157 
Basic  slag,  189,  222,  524 


553 


554 


INDEX 


Beehive  coke  oven,  114 

Benzine,  247 

Benzoic  acid,  259,  Ex.  170 

Bile,  321 

Bleaching,  396,  Ex.  285 

Bleaching  powder,  147,  Ex.  88     .   . 

Blue  prints,  238,  Ex   152 

Blue  vitriol,  233 

Boiled  oil,  399 

Bone  black,  113,  Ex.  68 

Borax,  198,  Ex.  119 

Bordeaux  mixture,  233,  416,  Ex.  304 

Boric  acid,  198 

test  for,  199,  Ex.  120 
Boron,  199 
Bread,  375 
Brick  making,  218 
Buhach,  413 
Bulgaris  milk,  361 
Butter,  264,  357 

renovated,  265 
Buttermilk,  358 
Butyric  acid,  264 

Caffeine,  286 
Calcite,  134 
Calcium,  138,  Ex.  81 
Calcium  carbonate,  134 
Calcium  cyanamide,  182,  529 
Calcium  hydroxide,  136 
Calcium  oxide,  135 
Calcium  phosphates,  188 
Calcium  sulphate,  139,  Ex.  82 
Calories,  327 
Calorimeter,  326 
Carbohydrates,  270 

changes  in  plant?,  306 

formation     in     plants,    301,     Ex. 

215 
Carbon,  111-120 

in  organic  matter,  115,  Ex.  66 

properties  of,  115 

reducing  agent,  115,  Ex.  67 
Carbon  bisulphide,  130,  414,  Ex.  77, 

Ex.  303 

Carbon  compounds,  123,  244 
Carbon  cycle,  128 
Carbon  dioxide,  123 

in  atmosphere,  73,  128,  Ex.  44 

in  nature,  128 

in  plant  life,  126 

preparation  of,  124,  Ex.  75 


Carbon  dioxide  —  (Continued) 

properties  of,  125 

test  for,  123,  Ex.  73 
Carbon  fixation,   126,   303,   Ex.   76, 

Ex.  216 

Carbon  monoxide,  129 
Carbon  tetrachloride,  408 
Carbonated  water,  125 
Carbonic  acid,  123,  Ex.  74 
Carborundum,  198 
Casein,  352,  Ex.  246 
Cashmere,  393 
Cast  iron,  221 
Catalysis,  84 
Catch  crops,  492 
Celluloid,  277 
Cellulose,  276 
Cement,  138,  Ex.  80 
Chalk,  134 
Charcoal,  animal,  113,  Ex.  68 

wood,  111,  Ex.  68 
Cheese,  359 

Chemical  changes,  57,  103 
Chemical  compounds,  58 
Chemical  tests,  109 
Chile  saltpeter,  161,  529,  Ex.  96 
Chlorine,  146,  Ex.  87 
Chlorophyll,  126 
Choke  damp,  129 
Citric  acid,  259 
City  sewage,  517 
Clay,  217,  Ex.  132 
Cleaning  materials,  404-409 
Coal,  113 
Coke,  114,  Ex.  69 
Cold  pack  method,  387,  Ex.  272 
Collodion,  277 
Combustion,  62,  Ex.  39 

spontaneous,  66 
Composts,  512 
Compounds,  56 
Condensed  milk,  359 
Contact  poisons,  412 
Copper,  230-234 

alloys  of,  231 

oxides  of,  232  . 

test  for,  234 

uses  of,  231 

Copper  hydroxide,  233,  Ex.  147 
Copper  sulphate,  233,  Ex.  144,  Ex. 

146 
Copperas,  223 


INDEX 


555 


Copper-plating,  231 
Coral,  134 

Corn  plant,  analysis  of,  295 
Cotton  cloth,  392,  Ex.  276 
mercerized,  392,  Ex.  278 
Covered  barnyard,  510 
Cream,  358 
Cream  of  tartar,  258 
Cream  separators,  356 
Crop  rotation,  495-500     . 
Crude  fiber,  294,  Ex.  209 

Dairy  farming,  543 

Davy's  safety  lamp,  120,  245 

Deep-tillage  machine,  467 

Definite  proportions,  57 

Deliquescence,  39 

Denitrification,  181,  434 

Destructive  distillation,  112 

Dextrin,  276 

Diamond,  111 

Dietary  standards,  341 

Dietary  studies,  347 

Diffusion  of  gases,  74,  Ex.  45 

Digestion,  318 
in  intestine,  320 
in  mouth,  318,  Ex.  226 
in  stomach,  319,  Ex.  227 

Digestion  experiments,  328 

Disinfectants,  389 

Distillation,  22 

Double  decomposition,  141 

Drainage,  443-449 

Dry  farming,  461 

Dry  matter  in  rations,  333 

Drying  oils,  265 

Dyeing,  395,  Ex.  284 

Dynamite,  254 

Earth  mulch,  458,  Ex.  336 
Efflorescence,  39 
Electrolysis  of  water,  48,  Ex.  29 
Electrotyping,  231 
Elements,  56 

essential,  313 
Enamel  paints,  402 
Energy,  available,  328 

net,  329 

Energy  materials,  325 
Energy  value  of  foods,  326 
Enzymes,  317,  321,  Ex.  225 
Epsom  salts,  211 


Equations,  98 
Essential  oils,  267,  Ex.  178 
Esters,  260,  Ex.  171 
Ether  extract,  293,  Ex.  208 
Ethereal  salts,  260 
Eudiometer,  54,  55 

Fall  plowing,  460 
Fallows,  463 
Farrington  tablets,  373 
Fats,  263,  265 

solvents  for,  408 
Fatty  acids,  263,  Ex.  177 
Feeding  farm  animals,  331-339 
Feeding  standards,  old,  337 
Feeds,  composition  of,  339 

fattening  requirements  of,  333 

growth  requirements  of,  332,  339 

maintenance  requirements  of,  331 

nutritive  ratio  of,  338 

palatability  of,  337 

work  requirements  of,  332 
Fermentation,  322 
Ferrous  sulphate,  223 
Fertilizers,  189,  530,  533-540,  542 
Fire  damp,  245 
Fixing  photographs,  237 
Flames,  116,  Ex.  71 

luminosity  of,  117,  Ex.  70 

structure  of,  118 
Fly  repellents,  414 
Food  adjuncts,  346 
Food  fads,  347 
Food  preservation,  by  drying,  385 

by  heat,  386 

by  refrigeration,  385 

chemical,  388,  Ex.  274 

cold  pack,  387,  Ex.  272 

in  strong  solutions,  386 
Foods,  341-349 

ash  of,  344 

digestibility  of,  345 

net  energy  of,  329 

palatability  of,  345 

requirements  of,  341 

uses  of,  324 

vitamines  in,  344 
Formaldehyde,  254,  417 
Formation,  heat  of,  127 
Formulas,  chemical,  97 
Fructose,  271,  Ex.  181 
Fruit  stains,  409 


556 


INDEX 


Fruits,  food  value  of,  346 
Fungicides,  416 
Fusion,  heat  of,  27 

Galvanizing,  212 

Gases,  are  substances,  75,  Ex.  46 

diffusion  of,  74,  Ex.  45 

kindling  temperature  of,  119,  Ex 
72 

liquefaction  of,  75 
Gasoline,  247 

for  cleaning,  408 
Gelatin,  284,  Ex.  203 
Glaciers,  421 
Glass,  195 

Glucose,  270,  Ex.  184 
Glutens,  282,  Ex.  197 
Glycerin,  253 
Grain  farming,  543 
Graphite,  111 
Green  manuring,  490^93 
Gums,  277,  Ex."l93 
Guncotton,  277 
Gunpowder,  207 

Harrows,  468 
Hartshorn,  171 
Hellebore,  412 
Human  foods,  341-349 
Hydrated  lime,  136,  Ex.  80 
Hydrocarbons,  245 
Hydrochloric  acid,  145,  Ex.  86 

test  for,  151,  Ex.  92 
Hydrocyanic  acid,  208,  414 
Hydrogen,  45-50 

from  water,  41 

occurrence  of,  47 

preparation  of,  45 

properties  of,  46 
Hydrogen  peroxide,  67,  102 
Hydrogen  sulphide,  108,  Ex.  64 

test  for,  109 

Hydrogenation  of  oils,  265 
Hydrosulphuric  acid,  108 
Hypo,  237 

Ice  making,  177 
Iceland  spar,  134 
Illuminating  gas,  114,  Ex.  69 
Indelible  ink,  Ex.  149 
Indicator,  157,  Ex.  94 


Ink  stains,  409 
Inks,  224,  259,  Ex.  149 
Inoculation  of  soils,  435 
Insecticides,  411-416 

gaseous,  414 

household,  414 
Intertillage,  471 
Invert  sugar,  273,  Ex.  183 
Iron,  220-224 

extraction  from  ores,  220 

rusting  of,  222 

sulphides  of,  224 

test  for,  224 

valence  of,  223 
Irrigation,  449-452 

in  humid  climates,  452 

methods  of,  450 

Japan  driers,  400 

Kaolin,  217 

Keeping  soil  sweet,  473-482 
Kindling  temperature,  63 
Koumiss,  361 

Lactic  acid,  258,  Ex.  165 
Lactometer,  371 
Lactose,  274 
Lampblack,  115 
Lapis  lazuli,  219 
Laughing  gas,  168,  Ex.  101 
1/avoisier,  49 
Lead,  226-229 

occurrence  of,  226 

oxides  of,  227 

properties  of,  226 

sugar  of,  108,  228 

tests  for,  228 

white,  228 

acetate,  108,  228 
arsenate,  228,  412 
ravening  agents,  375-382 
..egumes  in  soil  building,  424 
Lime,  135 

air-slaked,  138;  Ex.  80 

chloride  of,  147 

milk  of,  137 

slaked,  136,  Ex.  79 
ime  nitrogen,  182,  529 
-irne  sulphur,  412,  416,  Ex.  302 
Limekiln,  136 


INDEX 


557 


Limelight,  54,  118 
Limestone,  134 
for  soils,  473 
Limewater,  137 
Liming  soils,  477 
Limiting  factors,  437 
Linen,  393 

Linseed  oil,  265,  399,  Ex.  287 
Lipase,  320 
Litmus  paper,  86 
Litmus  test  for  soils,  475,  Ex.  345 
Luminosity  of  flames,  117 

Magnesium,  210 

occurrence  of,  210 

test  for,  211 

Magnesium  chloride,  211 
Magnesium  citrate,  259 
Magnesium  oxide,  210 
Magnesium  sulphate,  211 
Malt,  318 
Malt  sugar,  274 
Manure  shed,  510 
Marble,  134 
Market  gardening,  545 
Marl,  134,  479 
Marsh  gas,  244,  Ex.  155 
Matches,  185 
Mechanical  mixture,  58 
Metals,  158,  240 

recognition  of,  242 
Methane,  244,  Ex.  155 
Milk,  bacteria  in,  353 

composition  of,  350 

condensed,  359 

evaporated,  359 

powder,  359 

testing  of,  364 
Milk  and  products,  350-361 
Mineral  matter  in  plants,  312 
Mineral  waters,  38 
Miner's  safety  lamp,  120 
Mixed  farming,  544 
Mixed  fertilizers,  533-540 

buying,  534 

field  experiments,  536 

home-mixing,  533 
Mohair,  393 
Molecules,  92 
Mordants,  395,  Ex.  284 
Morphine,  286 
Mortar,  137 


Multiple  proportions,  87 
Muriate  of  potash,  526 

Naphtha,  247 
Negative,  237,  Ex.  151 
Net  energy  of  foods,  329 
Neutralization,  155,  Ex.  93 
Nicotine,  286 
Niter,  206 
Nitrates,  165,  Ex.  99 

test  for,  166 
Nitric  acid,  162,  164 

test  for,  166 

uses  of,  165 
Nitrification,  181 
Nitrites,  166,  Ex.  100 
Nitrocellulose,  277 
Nitrogen,  70 

fixation  of,  182,  435 

in  air,  70 

in  fertilizers,  527 

in  plants,  314 

occurrence  of,  71 

oxides  of,  167,  Ex.  101,  102 

properties  of,  70 
Nitrogen  cycle,  179 
Nitrogen-free  extract,  295 
Nitroglycerin,  253 
Nitro-lime,  182,  529 
Nitrous  acid,  166 
Non-metals,  158,  201 
Nutrition,  principles  of,  324-330 
Nutritive  ratio,  338 

Oils,  263 

essential,  267  / 
Oleic  acid,  264 
Oleomargarine,  264 
Orcharding,  546 
Organic  acids,  256-261 
Organic  'chemistry,  131,  244 
Organic  matter  in  soils,  423,  485 

functions  of,  486-488 

loss  of,  488 

restoring,  489 

Organic  nitrogen  compounds,  280-286 
Organic  salts,  260 
Osmosis,  310,  312,  Ex.  220 
Oxalic  acid,  258 
Oxides  and  oxidation,  61 
Oxygen,  49,  52-68 

occurrence  of,  67 


558 


INDEX 


Oxygen  —  (Continued) 

preparation  of,  48,  52,  Ex.  30 
properties  of,  53,  Ex.  31,  Ex.  32 
proportion  in  air,  67,  Ex.  41 

Oxy-hydrogen  blowpipe,  54 

Paints,  399-402 

Palmitic  acid,  264 

Paris  green,  233,  412 

Pasteurizing,  354 

Pectins,  277,  Ex.  193 

Pepsin,  320 

Peptones,  283,  Ex.  201 

Permanent  pastures,  547 

Persian  insect  powder,  413 

Petroleum,  246 

Phosphate,  acid,  190,  523,  Ex.  113 

bone,  521 

mineral,  522 

rock,  188,  522 

Thomas,  222 

with  manure,  524 
Phosphorescence,  184 
Phosphoric  acid,  186,  190,  Ex.  112 

salts  of,  187 

test  for,  190 
Phosphorus,  184 

m  fertilizers,  520 

occurrence  of,  188 

preparation  of,  185 

red,  185 

Physical  changes,  57,  103 
Pigments,  400 
Plant  growth,  298-307 
Plants,  composition  of,  289 

parasitic,  307 

Plaster  of  Paris,  139,  Ex.  82 
Plows,  464 
Porcelain,  217 
Positive,  237,  Ex.  151 
Potash,  206,  Ex.  124 

muriate  of,  526 
Potassium,  204-208 

in  fertilizers,  525 

occurrence  of,  204 

test  for,  208 
Potassium      carbonate,      206,      Ex. 

124 

Potassium  chlorate,  208,  Ex.  126 
Potassium  chloride,  205 
Potassium  cyanide,  208 
Potassium  hydroxide,  205,  Ex.  123 


Potassium  nitrate,  206 
Potassium  sulphate,  206,  526 
Potato  scab,  417,  Ex.  305 
Pottery,  217 
Priestley,  49 
Proteins,  280,  Ex.  194 

albumins,  283,  Ex.  198 

importance  of,  284 

in  human  diet,  343 

insoluble,  282,  Ex.  197 

manufacture  of,  306 

peptones,  283,  Ex.  201 

repair  material,  324 

tests  for,  281,  Ex.  196 
Ptomaines,  286 
Ptyalin,  319 
Pyrethrum  powder,  413 

Quartz,  193 
Quinine,  286 

Rations,  calculating,  334 

Reactions,  98 

Reagents,  98 

Reducing  agent,  115 

Reduction,  67,  Ex.  40 

Refrigeration,  385 

Rennin,  320 

Repair  material,  324 

Respiration  of  plants,  305,  Ex.  214 

Rollers,  470 

Roots,  bulbs,  and  tubers,  301 

Roots  dissolve  mineral  matter,  314, 

Ex.  223 
Rotation  of  crops,  495-500 

Sal  soda,'  150 

Salicylic  acid,  259 

Salt,  144,  145,  Ex.  85,  Ex.  86 

Saltpeter,  161,  206,  529,  Ex.  96 

Salts,  155,  156,  157 

Sand,  193,  Ex.  115 

Saponification,  267 

Scheele,  49 

Scouring  soaps,  407,  Ex.  296 

Seeds,  germination  of,  298,  Ex.  211, 

Ex.  213 

Sheep  dips,  414 
Shells,  134 
Short  fallows,  464 
Shortening,  381,  Ex.  269 
Silica,  193 


INDEX 


559 


Silicates,  decomposing,  197 

natural,  196,  Ex.  118 

test  for,  197 

Silicic  acid,  195,  Ex.  116 
Silicon,  194 
Silk,  394 
Silver,  235-238,  Ex.  148 

test  for,  238,  Ex.  153 
Silver  chloride,  236 
Silver  nitrate,  236 
Silver  sulphide,  235 
Silver-plating,  236 
Skim  milk,  355 

Slaked  lime,  136,  Ex.  79,  Ex.  80 
Slow  oxidation,  64,  Ex.  38 
Soap  powders,  407 
Soaps,  266,  404-406,  407 
Soda  water,  125 
Sodium,  145,  148-151,  Ex.  89 

test  for,  151 

Sodium  benzoate,  260,  Ex.  170 
Sodium  bicarbonate,  150,  Ex.  91 
Sodium  borate,  1S8,  Ex.  119 
Sodium  carbonate,  150,  Ex.  91 
Sodium  fluoride,  415 
Sodium  hydroxide,  149,  Ex.  90 
Sodium  sulphate,  149 
Sodium  sulphite,  150 
Soils,  420-500 

acidity  of,  473-478 

animal  life  in,  424 

chemical  analysis  of,  437 

classification  of,  427 

formation  of,  420-425 

inoculation  of,  435 

keeping  sweet,  473-482 

liming  of,  477 

limiting  factors  in,  437 

litmus  test  of,  475 

mineral  elements  in,  436 

physical  make-up  of,  426 

Truog  test  of,  476,  Ex.  346 

water  in,  440-452 
Specific  heat,  29 
Spontaneous  combustion,  66 
Spots  and  stains,  409 
Spring  plowing,  459 
Stable  manure,  501-517 

applying,  513 

composition  of,  502 

composting  of,  512 

factors  affecting  value  of,  503 


Stable  manure  —  (Continued) 

importance  of,  501 

leaching  of,  508 

liquid,  value  of,  506 

losses  in,  505 

phosphates  with,  524 

preservatives  with,  507 

results  with,  516 

sheds  for,  510 

valuation  of,  501 
Starch,  274,  Ex.  186 
Steapsin,  320 
Stearic  acid,  264 
Steel,  222 
Stereotyping,  232 
Stomachic  poisons,  412 
Strychnine,  286 
Sublimation,  176,  Ex.  107 
Sugar,  cane,  272,  Ex.  184 

fruit,  271,  Ex.  181 

grape,  270,  Ex.  184 

invert,  273,  Ex.  183 

malt,  274 

milk,  274 

Sugar  of  lead,  108,  228 
Sulphides,  81,  Ex.  51 
Sulphur,  78-88 

occurrence  of,  81 

preparation  of,  79 

properties  of,  79 

two  acids  of,  106,  Ex.  63 
Sulphur  dioxide,  82,  Ex.  52 
Sulphur  trioxide,  83,  Ex.  53 
Sulphureted  hydrogen,  108 
Sulphuric  acid,  85,  105,  107,  Ex. 
54,  Ex.  55 

test  for,  109 
Sulphurous  acid,  104,  Ex.  61 

test  for,  109 
Summer  fallows,  463 
Superphosphate,  523 
Symbols,  94 
Synthesis,  56 

Tannic  acid,  259,  Ex.  169 
Tartaric  acid,  258 
Textiles,  392-395 
Thomas  phosphate,  222 
Tillage,  455-471 

aerates  soil,  456 

conserves  moisture,  457,  Ex.  336 

destroys  weeds,  460 


560 


INDEX 


Tillage  —  (Continued") 

harrowings  468 

increases  feeding  ground,  455 

increases  water,  456 

plowing,  464 

rolling,  470 

Tobacco  insecticides,  413 
Truog  test,  476,  Ex.  346 
Trypsin,  320 
Types  of  farming,  542-547 

all  crops  sold,  542 

dairying,  543 

fat  stock,  544 

grain,  543 

market  gardening,  545 
'  mixed,  544 

orcharding,  546 

special  crops,  545 

Ultramarine,  218 
Urea  in  manure,  507 

Valence,  102 

Vaporization,  heat  of,  27 
Varnishes,  402 

black,  403 

Vehicles  for  paints,  399,  Ex.  287 
Vinegar,  256 

quick  process,  257 
Vitamines,  344 

Washing  soda,  150,  407,  Ex.  91 
Water,  21-44 

accelerates    chemical    action,    35, 
Ex.  16 

amount  used  by  plants,  309 

boiled  for  drinking,  36 

boiling  point  changed,  35,  Ex.  15 

composition  of,  54 

contamination  of,  36,  Ex.  17 

decomposition  of,  40,  Ex.  22 

distillation  of,  22,  Ex.  2 

effect  of  pressure  on,   25,   Ex.   6, 
Ex.  7 

electrolysis  of,  48,  Ex.  29 

freezing  of,  24,  Ex.  5 

functions  of,  in  plant,  311,  Ex.  221 

hard,  37,  140,  405,  Ex.  18,  Ex.  83, 
Ex.  84 

heat  of  fusion,  27,  Ex.  9 


Water  —  (Continued') 

heat  of  vaporization,  27,  Ex.  10 

hydrogen  from,  41,  Ex.  22 

importance  to  plants,  309,  Ex.  219 

in  organic  matter,  38,  Ex.  19 

maximum  density  of,  24 

mineral,  38 

mineral  matter  in,  22,  Ex.  1 

never  pure  in  nature,  21 

of  crystallization,  39,  Ex.  20 

poor  conductor,  28,  Ex.  11 

potable,  35,  Ex.  17 

properties  of,  23,  Ex.  3 

rain,  22,  Ex.  1 

solvent  action  of,  34,  Ex.  12,  Ex.  13, 
Ex.  14 

three  states  of,  24 

used  to  establish  standards,  25 

vapor  in  air,  72,  Ex.  43 
Water  gas,  130 
Water  glass,  194,  Ex.  117 
Water  paints,  401 
Water  table,  440 
Water-soluble  vitamines,  343 
Weathering  of  rocks,  420,  423,    Ex. 

307 

Weeds  destroyed  by  tillage,  460 
Welding,  222 
Welsbach  burner,  118 
Whale  oil  soap,  413 
What  to  eat,  348 
White  lead,  228,  400 
White  wine  vinegar,  257 
Whitewash,  137,  401 
Wind  action,  422 
Wintergreen,  oil  of,  260,  Ex.  172 
Wood  ashes,  206,  527 
Wool,  393,  Ex.  280,  Ex.  282 

test  for,  394 

Work,  food  requirements  for,  332 
Wrought  iron,  221 

Yeast,  in  bread  making,  376,  Ex.  263 

Zinc,  211-213  • 

metallurgy  of,  212 

preparation  of,  211 

properties  of,  212 

tests  for,  213 
Zinc  oxide,  212,  400 


HDYYUOY 

Alfrled 


Everyday  chemistry 


Educ. 


LID. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


YB  36027 


INTERNATIONAL  ATOMIC  WEIGHTS  (1914) 
O-16 


Aluminum      .    .    .    .  Al 

Antimony Sb 

Argon A 

Arsenic As 

Barium Ba 

Beryllium      ....  Be 

Bismuth Bi 

Boron B 

Bromine Br 

Cadmium Cd 

Casium Ca 

Calcium Ca 

Carbon C 

Cerium Ca 

Chlorine Cl 

Chromium     .    .    .    .  Cr 

Cobalt ;  Co 

Columbium  .  .  ,  §  Ob 
Copper.  ... 
Dysprosium  .  . 
Erbium  .  .  . 
Europium .  .  . 
Fluorine  ... 

Gadolinium  ....  Ud 

Gallium     .....  Ga 

Germanium  .    ...  Go 

Gold 

Helium «•-' 

Holmium 

Hydrogen BL 

Indium In 

Iodine I 

Indium IT 

Iron Fe 

Krypton Kr 

Lanthanum  ....  La 

Lead Pb 

Lithium    .....  Li 

Lutecium Lu 

Magnesium    ....  Mg 

Manganese    ....  Mn 

Mercury Hg 


27.1          Molybdenum ....  Mo     96.0 

120.2  Neodymium   ....  Nd  144.3 

39.88        Neon Ne      20.2 

74.96        Nickel Ni      58.68 

137.37         Niton  (radium  emanation)  Nt  222.4 

9.1          Nitrogen N        14.01 

208.0  Osmium Os  190.9 

11.0          Oxygen O        16.00 

79.92        Palladium Pd  106.7 

112.40        Phosphorus     .    .    .    .  P        31.04 

132.81        Platinum Pt  195.2 

40.07        Potassium K       39.10 

12.00        Praseodymium    .    .    .  Pr  140.6 

140.25        Radium Ra  226.4 

35.40        Rhodium Rh  102.9 

62.0          Rubidium Rb      85.45 

iuthenium     .    .    .    .  Ru  101.7 

marium Sa  150.4 

<**iri Sc       44.1 

So       79.2 

37.7  3i        28.3 

52.0  .    .    .    .  Ag  107.88 

19.0          S  .    .    .    .  Na      23.00 

157.3  St                    .    .    .    .  Sr       87.63 
69.9                                 .    .    .    .  S         32.07 
72.5          j.                 Ta  181.5 

197.2  n Te  127.5 

m Tb  159.2 

im Tl  204.0 

am Th  232.4 

114.6  urn Tm  168.5 

126.92        Tin Sn  119.0 

193.1  Titanium Ti       48.1 

65.84        Tungsten W  184.0 

82.92  Uranium U  238.5 

139.0          Vanadium V        61.0 

207.10        Xenon Xe  130.2 

6.94        Ytterbium  (Neoytter- 

174.0  bium) Yb  172.0 

24.32        Yttrium Yt      89.0 

54.93  Zinc Zn      65.37 

200.6          Zirconium Zr       90.6 


